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Show 139 i n t h e l o w e r G r e a t B l u e . The cup c o r a l s a r e e s p e c i a l l y a b u n d a n t. N e a r t h e m i d d l e of t h e u n i t t h e r e a r e a f ew d i s c o n t i n u o u s b a n ds of b l a c k c h e r t which r a n g e f r o m 4 t o 6 i n c h e s in t h i c k n e s s, s p a c e d at i n t e r v a l s of 1 t o 3 f e e t . This s e q u e n c e i s about 425 f e et t h i c k and i s c r u d e l y l a m i n a t e d by d i s p e r s a l of 5° to 6 - f o o t b e d s of d a r k g r a y , r o u g h w e a t h e r i n g l i m e s t o n e s a m o n g c h e r t y , b l u e - g r a y, m a s s i v e l i m e s t o n e s which c o m p r i s e the g r e a t e r p a r t of t h is i n t e r v a l . T h e b a s e of t h e G r e a t Blue f o r m a t i o n i s g r a d a t i o n a l with the u n d e r l y i n g Humbug f o r m a t i o n and i s d r a w n at a p o i n t w h e r e q u a r t z i t es a n d s a n d s b e c o m e a p r o m i n e n t , but not d o m i n a n t , l i t h o l o g y . Very l i t t l e s a n d i s d i s p e r s e d in t h e b a s a l b e d s of t h e G r e a t Blue f o r m a t i o n. F i e l d i d e n t i f i c a t i o n - The m a s s i v e c h a r a c t e r of t h e u n i t s of the G r e a t Blue f o r m a t i o n i s v e r y d i s t i n c t i v e , a s i s t h e p r e s e n c e of l a r ge h o r n c o r a l s in t h e u p p e r and l o w e r m e m b e r s of t h e f o r m a t i o n. Some b l a c k c h e r t i s i n t h e b a s a l b e d s of t h e l o w e r and u p p e r l i m e s t o n e m e m b e r s , and i t s p r e s e n c e m a y s u g g e s t t h e M a d i s o n f o r m a t i on e s p e c i a l l y if t h e o u t c r o p i s s m a l l in a r e a . G e n e r a l l y , the l a r g e h o rn c o r a l s s e r v e to c o m p l e t e the i d e n t i f i c a t i o n . Thick c o l o n i a l c o r a ls s e r v e a s an a i d f o r i d e n t i f y i n g the u p p e r p a r t of the l o w e r l i m e s t o ne m e m b e r . The two l i m e s t o n e u n i t s a r e d i f f i c u l t to s e p a r a t e without t h e p r e s e n c e of t h e I n t e r v e n i n g C h i u l o s s h a l e . The b l u e - g r a y c o l or i s r a t h e r u n i f o rm in t h e two l i m e s t o n e s , and f r e s h s u r f a c e s a r e only 140 s l i g h t l y d a r k e r t h a n the w e a t h e r e d r o c k . Black s h a l e on b o th s i d e s of a t h i c k q u a r t z i t e u n i t s e r v e s to i d e n t i f y the C h i u l o s as d o e s t h e C a l a m i t e s s p . n e a r the c e n t e r of t h e q u a r t z i t e b e d s. D a r k b r o w n l im on I t e - s t a i n e d z o n e s in t h e c r o s s - b e d d e d q u a r t z i te h a v e y i e l d e d t h e s e p l a n t f o s s i l s . The u p p e r s h a l e c o n t a i n s m a ny b r a c h i o p o d s . Age and c o r r e l a t i o n - F o s s i l s w e r e c o l l e c t e d f r o m s i x t e en l o c a l i t i e s ( A p p e n d i x B 9 P l a t e III) in the G r e a t Blue f o r m a t i o n. W a l t e r S a d l i c k e x a m i n e d the s p e c i m e n s and r e p o r t e d: L o w e r l i m e s t o n e m e m b e r: M - 4 , F a b e r o p h y l l u m s p. M - 8 , F a b e r o p h y l l u m s p. S p i r i f e r ( l a r g e ) S p i r i f e r h a y d e n s i s ? G a s t r o p o d S p i r i f e r o l d n„ s p . aff. S p i r i f e r b i f u r c a t us ( p o o r l y p r e s e r v e d) M - l l , Small s y r i n g o p o r i d c o r al L i t h o s t r q t i o n s p. L i n o p r o d u c t u s aff. S t r i a t i f e r a b r a z e r i a n us F a b e r o p h y l l u m ? M - 1 4 D i a p h r a g m u s ? v e r y p o or M - 1 5 L i n o p r o d u c t u s n . s p . aff. S t r i a t i f e r a b r a z e r i a n us P r o d u c t u s aff. a r k a n s a n us A n t i q u a t i o n a n . s p. D i a p h r a g m u s ? s p. S p i r i f e r aff. S. i n c r e b e n c e ns M-16 L i n o p r o d u c t u s aff. L. m a g n i s p i n us M - 2 2 L i n o p r o d u c t u s n„ s p . aff. S t r i a t i f e r a b r a z e r i a n us L i t h o s t r o t i o n s p. E u m o p h a l i d g a s t r o p od M - 2 3 S p i r i f e r o l d n. s p . aff. S p i e i f e r b i f u r c a t us j ^ ^ P £ £ 2 J H ^ l u 5 P^eiformis P i e t y o c l o s t i d s aff. D. i n f l a t us 141 R o l a n d W. B r o w n i d e n t i f i e d C a l a m i t e s s p n f r o m p l a n t r e m a i ns i n t h e q u a r t z i t e z o n e of t h e C h i u l o s s h a l e m e m b e r . U p p e r l i m e s t o n e m e m b e r: M°12 S t e J a t i f e r a b r a z e r i a n us E c h i n o c c o n c l r a s aff. geacv JEgygatsis Die t y p e Lostus -aff. P.- b u r l i n g t o n e n s i s C o m p o s i t a t r i n u c l e a s&. C l e i o t n y r : u K n a n . s p. R e t i c u i a r i n a s p i n o s a , s m a l l f o rm M ~ l 3 R h i p i d o m e l b a aff. c a r b o n a r i a M - 1 9 L i t h o s t r o t i o n e 11a s p . C a n i n i a . ? T h e f a u n a i n d i c a t e s t h a t t h e G r e a t B l u e f o r m a t i o n i s b a s a l U p p er M i s s i s s i p p i a n ( C h e s t e r i a n ) in a g e. T h e G r e a t Blue f o r m a t i o n i s t h e a p p r o x i m a t e age e q u i v a l e n t to t h e O c h r e M o u n t a i n of N o l a n (1935) at Gold H i l l , Utah; t h e u p p e r p a rt of t h e C h a i n m a n s h a l e at E l y , Nevada; the g r e a t e r c e n t r a l p o r t i o n of t h e B r a z e r f o r m a t i o n in n o r t h e a s t e r n Utah. S a d l i c k i n d i c a t e s tn&fche w e s c o n s i d e r i n g e l e v a t i n g t h e G r e at B l u e f o r m a t i o n to g r o u p s t a t u s and n a m i n g the l o w e r l i m e s t o n e the F l u x l i m e s t o n e ( l o c a t i o n in n o r t h e r n S i a n s b u r y M o u n t a i n s , Utah). The C h i u l o s m e m b e r Is p r o b a b l y e q u i v a l e n t to t h e L o n g T r a i l s h a le of t h e t y p e G r e a t B l u e l i m e s t o n e In t h e O q u i r r h M o u n t a i n s and the H e r a t s h a l e m e m b e r of t h e O c h r e M o u n t a i n l i m e s t o n e In t h e P e ep C r e e k M o u n t a i n s. 142 P E N N S Y L V A N I A SYSTEM O q u i r r h f o r m a t i on T h e O q u i r r h f o r m a t i o n i s in f a u l t c o n t a c t with t h e U p p e r l i m e s t o ne m e m b e r of t h e G r e a t B l u e f o r m a t i o n . The O q u i r r h i s e x p o s e d only a l o n g t h e n o r t h e r n l i m i t s of t h e m a p p e d a r e a . No s t u d y was m a d e of t h e O q u i r r h , s i n c e n e i t h e r t h e t o p n o r t h e b a s e of t h e f o r m a t i o n is e x p o s e d . The r o c k s c o m p r i s i n g the O q u i r r h a r e s i i t y g r a y l i m e s t o ne a n d tan t o s l i g h t l y p u r p l i s h t i n t e d q u a r t z i t e s . B r y o z o a n f r a g m e n ts w e r e r e c o v e r e d f r o m s o m e of t h e t a n s i l t y l i m e s t o n e u n i t s. I n t h e n o r t h e n d of t h e W e s t L o o k o u t H i l l s a l l o c h t h o n o u s b l o c ks of s t r a t a , t e n t a t i v e l y a s s i g n e d to t h e O q u i r r h f o r m a t i o n , a r e i n t h r u st c o n t a c t with s t r a t a of O r d o v i c i a n to M i s s i s s i p p i a n a g e. C r e t a c e o u s o r T e r t i a r y r e d b e d s a n d c o n g l o m e r a t e u n c o n f o r m a b ly o v e r l i e s t e e p l y d i p p i n g b e d s of t h e O q u i r r h f o r m a t i o n in t h e n o r t h w e st c o r n e r of t h e a r e a. 143 R E S U M I C O F P R E C A M B R I A N A N D P A L E O Z O I C H I S T O RY P r e c a m b r i a n T h e a d v a n c i n g C a m b r i a n s e a s m o v e d f r o m s o u t h w e s t to n o r t h e a s t a l o n g t r o u g h s p r o b a b l y f o r m e d d u r i n g l a t e P r e c a m b r i a n t i m e. As t h e t r o u g h s d e e p e n e d , the b a s a l C a m b r i a n s e d i m e n t s b e c a m e l e ss a n d l e s s c o n f o r m a b l e with u n d e r l y i n g P r e c a m b r i a n s t r a t a. P r i o r to d e p o s i t i o n of b a s a l C a m b r i a n s t r a t a in t h e S h e e p r o ck a r e a , an a r e a of c o n s i d e r a b l e r e l i e f m u s t h a v e b e e n p r e s e n t in or a r o u n d t h e S h e e p r o c k r e g i o n . T i i l i t e s t e s t i f y to t h e p r e s e n c e of a h i g h l a n d , though i t m a y h a v e b e e n f a r r e m o v e d f r o m the S h e e p r o ck v i c i n i t y , as a r e the i c e c e n t e r s of p r e s e n t day g l a c i a t i o n r e m o v ed f r o m the t e r m i n a l e d g e s of a s s o c i a t e d i c e s h e e t s . S l a t e s and q u a r t z i t es of the S h e e p r o c k s e r i e s , b e l o w t h e D u t c h P e a k t i l l i t e , i n d i c a t e that t h o s e r o c k s a r e p r o b a b l y of c o n t i n e n t a l a n d l a c u s t r i n e o r i g i n . The S h e e p r o c k s e r i e s c o n t a i n s , as a g r a d a t i o n a l u n i t , the D u t c h P e ak t i l l i t e . The S h e e p r o c k s e r i e s i s c o n s i d e r e d to b e y o u n g e r t h a n the B i g C o t t o n w o o d s e r i e s . The M i n e r a l F o r k t i l l i t e , p r o b a b l y e q u i v a l e nt i n a g e to t h e Dutch P e a k t i l l i t e , u n c o n f o r m a b l y o v e r l i e s the B i g C o t t o n wood s e r i e s in t h e W a s a t c h r e g i o n s o m e 60 m i l e s e a s t of the S h e e p r o ck a r e a . The Big C o t t o n w o o d s e r i e s m a y be B e i t i a n in a g e a n d c o u ld c o n f o r m a b l y u n d e r l i e the s t r a t a of t h e S h e e p r o c k s e r i e s with g r a d a t i o n al c o n t a c t . The M u t u a l f o r m a t i o n i s t h e y o u n g e s t of t h e P r e c a m b r i an 144 r o c k s r e c o g n i z e d in the W a s a t c h r e g i o n . In t h e S h e e p r o c k a r e a the p r e s e n c e of s t r a t a with d i f f e r i n g t h i c k n e s s e s and i i t h o i o g y a b o v e the S h e e p r o c k s e r i e s s u g g e s t s an u n c o n f o r m i t y , and t h e s e s t r a t a a re q u e s t i o n a b l y d e s i g n a t e d the M u t u a l f o r m a t i o n. T h e T i n t i c q u a r t z i t e i s t h e b a s a l C a m b r i a n f o r m a t i o n in the S h e e p r o c k r e g i o n and n i n e o n f o r m a b l y o v e r l i e s r o c k s a s s i g n e d to the M u t u a i ( ? ) f o r m a t i o n. T h e s e q u e n c e of e v e n t s f o r t h e P r e c a m b r i a n a r e: 1. F o l d i n g , i n t r u s i o n and m e t a m o r p h i s m of A r c h e an ( F a r m i n g t o n Canyon C o m p l e x ) r o c k s. 2. D e p o s i t i o n of L i t t l e W i l l ow s e r i e s. 3 . D e f o r m a t i o n of L i t t l e W i l l ow s e r i e s . 4 . D e p o s i t i o n of Big C o t t o n w o o d s e r i e s in g e o - s y n c l i n a l o r s h e l v i n g a r e a s to t h e w e s t. 5 . D e p o s i t i o n of S h e e p r o c k s e r i e s on s h e l f in t h e g e o s y n c l i n e and on r i s i n g h i n g e a r ea a l o n g W a s a t c h f r o n t. 6. G l a c i a t i o n , p r o b a b l y of t h e P i e d m o n t t y p e , which e r o d e d m a t e r i a l f r o m t e r r a n e c o m p o s e d m a i n l y of s t r a t a of t h e L i t t l e W i l l ow and B i g C o t t o n w o o d s e r i e s. 7. Slight u p l i f t and r e j u v e n a t i o n of e r o s i o n which f u r° n i s h e d s e d i m e n t s f o r the M u t u a l f o r m a t i o n. 145 8. Advance of m a r i n e c o n d i t i o n s i n t o S h e e p r o ck a r e a o v e r a s i n k i n g c o n t i n e n t a l m a r g i n which p r o d u c e d a b a s a l C a m b r i a n q u a r t z i t e o v e r d i s c o r d a n t s t r a t a of t h e y o u n g e r P r e c a m b r i a n. C a m b r i a n C a m b r i a n s e a s g r a d u a l l y t r a n s g r e s s e d the r e g i o n f r o m s o u t h w e st t o n o r t h e a s t . C o n t i n e n t a l s e d i m e n t a t i o n in t h e b a c k v a l l e y s and d e p r e s s i o n s c o n t i n u e d a s the s e a s s o r t e d the s h o r e l i n e s e d i m e n t s to f o r m the b a s a l C a m b r i a n q u a r t z i t e s and c o n g l o m e r a t e s . The h i g h l a n ds f l a n k i n g the s e a w a y s w e r e c o n t i n u a l l y b e i n g d e f o r m e d by i s o s t a t i c a d j u s t m e n t s , and i t i s p o s s i b l e t h a t c e r t a i n u n i d e n t i f i e d s e q u e n c e s of c o n t i n e n t a l C a m b r i a n s e d i m e n t s w e r e c o n t i n u a l l y b e i n g t r a n s g r e s s ed by the e x p a n d i n g C a m b r i a n s e a s . The b a s a l c o n g l o m e r a t e s w e r e p r o b a b l y d e r i v e d f r o m t h e h i g h l a n d s to the e a s t and f r o m i s l a n d a r e as w i t h i n the r e g i o n of i n v a s i o n , s u c h a s in e a s t - c e n t r a l N e v a d a , and n o r t h w e s t e r n and n o r t h - c e n t r a l U t a h . Seas c o n t i n u e d to o c c u p y the r e g i o n d u r i n g t h e r e m a i n d e r of C a m b r i a n t i m e . During M i d d l e and L a t e C a m b r i a n t i m e s s o m e a r e a s s h o a l e d s u f f i c i e n t l y to a l l ow f o r m a t i o n of o o l i t e s and o t h e r p r i m a r y s h a l l o w w a t e r f e a t u r e s . There w e r e t i m e s when t h e c o m p e t e n c y of t h e m a r i n e w a t e r s i n c r e a s e d or when g r e a t e r s u p p l y of s l i t s w e r e a v a i l a b l e f o r m a r i n e d e p o s i t i o n. T h i s type of c h e m i c a l and m i l d c l a s t i c d e p o s i t i o n p e r s i s t e d at i n t e r v a ls t h r o u g h o u t t h e C a m b r i a n and i n t o t h e O r d o v i c i a n. 146 O r d o v i c i a n O r d o v i c i a n e n v i r o n m e n t a l c o n d i t i o n s w e r e m a i n l y s i m i l a r to t h e C a m b r i a n u n t i l M i d d l e O r d o v i c i a n t i m e . During Middle O r d o v i c i a n t i m e , the s e a s s l o w l y w i t h d r e w and a s h a l e - q u a r t z i te s e q u e n c e was d e p o s i t e d in i t s w a k e . The p e r i o d of t h i s w i t h d r a w al was r e l a t i v e l y slow, but was c o m p l e t e d d u r i n g M i d d l e O r d o v i c i an t i m e . A t r a n s g r e s s i o n of m a r i n e w a t e r s i n t o t h e r e g i o n o c c u r r ed a g a i n i n l a t e O r d o v i c i a n . The l a t e O r d o v i c i a n F i s h H a v e n s ea o c c u p i e d the r e g i o n r a t h e r r a p i d l y . The a b s e n c e of an o v e r l y i n g s h a le i n d i c a t e s a r a p i d t r a n s g r e s s i o n . The l a c k of f r a g m e n t s of t h e E u r e ka o r Swan P e a k q u a r t z i t e s in t h e b a s a l u n i t of t h e F i s h H a v e n d o l o m i te i n d i c a t e s t h a t an i n s u f f i c i e n t a m o u n t of t i m e was a v a i l a b l e f o r even p a r t i a l l i t h i f i c a t i o n of t h e s a n d s . The s o u r c e of the O r d o v i c i a n s a n ds was m o s t l i k e l y t h e b a s a l C a m b r i a n q u a r t z i t e s of t h e h i g h l a n d s e a st of t h e ' h i n g e l i n e ' o r e a s t e r n b o r d e r of t h e g e o s y n c l i n e . The t h i c k e s t s a n d s ( s e e F i g u r e 5) c o i n c i d e with a r e a s of g r e a t e s t C a m b r i an ( s e e F i g u r e 4) an d L o w e r O r d o v i c i a n s e d i m e n t a t i o n . The t h i c k er p o r t i o n s of t h e O r d o v i c i a n s a n d s m a y be c o n s i d e r e d to o c c u p y the d e e p e s t p o r t i o n s of t h e C a m b r o - O r d o v i c l a n g e o s y n c l i n e , where d i f f e r e n t i a l c o m p a c t i o n was g r e a t e s t . C o n d i t i o n s c o n d u c i v e to d o l o m i t i c s e d i m e n t a t i o n p e r s i s t e d to t h e end of O r d o v i c i a n t i m e. S i l u r i an L o w e r and M i d d l e S i l u r i a n r o c k s a r e m i s s i n g o r a r e r e p r e s e n t ed 147 by only a f ew f e e t of b e d s . A b s e n c e of s t r a t a r e p r e s e n t i n g m o s t of t h i s t i m e m a y be e i t h e r the r e s u l t of n o n - d e p o s i t i o n o r d e p o s i t i o n and r e m o v a l by e r o s i o n . The v a r i a t i o n of t h i c k n e s s of the o v e r l y i ng Sevy d o l o m i t e of D e v o n i a n age i n d i c a t e s c o n s i d e r a b l e r e l i e f on the b u r i e d s u r f a c e , which s e p a r a t e s the S i l u r i a n f r o m the D e v o n i a n. L o w e r and M i d d l e S i l u r i a n t i m e p r o b a b l y was one of n o n - d e p o s i t i o n. D e v o n i an E a r l y D e v o n i a n t i m e was c h a r a c t e r i z e d by r e l a t i v e l y s h a l l o w s e as and t i d a l f l a t s . Slight u p l i f t m u s t h a v e b e e n p r e s e n t a l o n g t h e e a s t e rn f l a n k s of t h e g e o s y n c l i n e . O r d o v i c i a n and C a m b r i a n q u a r t z i t e s w e re b e i n g e r o d e d and r e d e p o s i t e d In t h e d o l o m i t e m u d s by wind a c t i o n. F i s h r e m a i n s in t h e b a s a l D e v o n i a n d o l o m i t e s u g g e s t an e s t u a r i ne e n v i r o n m e n t . The d i s p e r s a l of f r o s t e d and r o u n d e d q u a r t z g r a i ns i n t h e L o w e r D e v o n i a n d o l o m i t e I n d i c a t e s winds s u f f i c i e n t l y s t r o n g to h a v e c a r r i e d t h e s a n d , f r o m an a r e a n e a r the ' h i n g e line* i n c e n t r al U t a h ; t o a p o i n t a s f a r west a s e a s t e r n N e v a d a . This r e q u i r e s e a s t - t o - w e s t w i n d s , which m a y be q u e s t i o n a b l e . A p o s s i b l e a l t e r n a t i v e s o u r ce of t h e w i n d - f r o s t e d s a n d s c o u l d be i s l a n d a r e a s d e v e l o p e d in the r e g i o n of t h e M a n h a t t a n G e a n t i c l i n e to t h e w e s t. M i d d l e D e v o n i a n t i m e was m a r k e d by d e e p e r w a t e r s and o s c i l l a t i o n s which p r o d u c e d e n v i r o n m e n t a l c h a n g e s s u f f i c i e n t to c a u s e c o l o r a l t e r n a t i o n s in c o a r s e r d o l o m i t i c s e d i m e n t s . Middle D e v o n i a n was p r o b a b l y a p e r i o d of r e l a t i v e q u i e s c e n c e with h i g h l a n ds 148 r e m a i n i n g s t a t i c . Late D e v o n i a n was a p e r i o d of g e n e r a l u n r e st i n t h e e a s t e r n m a r g i n of the g e o s y n c l i n e and a l o n g a s a l i e n t e x t e n d i n g f r o m Salt L a k e and P r o v o a r e a w e s t w a r d to b e y o n d t h e N e v a d a - U t a h l i n e . The r i s i n g l a n d s f u r n i s h e d d e b r i s to t h e d e e p e r p o r t i o ns of t h e g e o s y n c l i n e . The ' S t a n s b u r y S a l i e n t 1 , a p e n i n s u l a r - l i k e p r o m i n e n c e , r e c e i v e d e x t e n s i v e c o n g l o m e r a t e s f r o m the r i s i n g h i g h l a n d s. The s a n d s I n t e r t o n g u e with c a r b o n a t e s f a r t h e r w e s t . The s a n d t o n g u es a n d l e n s e s l a c k u n d e r l y i n g o r o v e r l y i n g s h a l e s , which s e e m s to be c h a r a c t e r i s t i c of s l o w e r r e g r e s s i o n s and t r a n s g r e s s i o n s of s ea w a t e r s . It i s , t h e r e f o r e , a s s u m e d t h a t t h e s a n d s of t h e Upper D e v o n i a n p e r i o d w e r e p r i n c i p a l l y of f l u v i a l o r i g i n a n d , t h e r e f o r e, would b e c o n f i n e d to a r e a s n e a r e r the ' h i n g e l i n e 1 , the s o u r c e a r e a. M i s s i s s i p p i a n M i s s i s s i p p i a n t i m e o p e n e d with e x t e n s i v e s e a w a y s which c o v e r ed m u c h m o r e a r e a t h a n m o s t of t h e p r e v i o u s P a l e o z o i c s e a s . F o l l o w i ng M a d i s o n t i m e , with i t s e x t e n s i v e s e a w a y s , s i l t s and s a n d s b e c o me m o r e p r o m i n e n t , i n d i c a t i n g t h a t r i s i n g h i g h l a n d s w e r e a g a i n b e i ng f o r m e d . F o l l o w i n g t h e c h e m i c a l and m i l d l y c l a s t i c d e p o s i t i o n of M i d d l e M i s s i s s i p p i a n w e r e the p e r i o d s of a l t e r n a t i n g c a r b o n a t e and c l a s t i c d e p o s i t i o n in l a t e M i d d l e and U p p e r M i s s i s s i p p i a n t i m e s. An e x t e n s i v e , n e a r l y e a s t - w e s t , n a r r o w t r o u g h d e v e l o p e d in m i d - G r e a t B l u e t i m e and a b l a c k s h a l e e n v i r o n m e n t p r e v a i l e d . C h e r t y, b l a c k s h a l e c o n t a i n i n g m a r c a s i t e I n d i c a t e s a t o x i c e n v i r o n m e n t. 149 C r o s s - b e d d e d o r t h o q u a r t z i t e s , b e a r i n g C a l a m i t e s , a r e i n t e r c a l a t ed with t h e b l a c k s h a l e . C l a s t i c l i m e s t o n e with a b u n d a n t s i l t and f r a g m e n t s of w a t e r - w o r n b r a c h i o p o d s i n d i c a t e s h a l l o w w a t e r s and p r o x i m i t y to l a n d . Rocks r e p r e s e n t i n g the U p p e r M i s s i s s i p p i an p e r i o d h a v e b e e n r e m o v e d by e r o s i o n o r a r e b u r i e d b e n e a t h P l i o c e n e - P l e i s t o c e n e and R e c e n t a l l u v i um in t h e S h e e p r o c k a r e a. P e n n s y l v a n i a n and l a t e r p e r i o ds M a r i n e c o n d i t i o n s p r e v a i l e d f o r the g r e a t e r p a r t of P e n n s y l v a n i an t i m e . S u b s i d e n c e b e g a n in t h e O q u i r r h B a s i n , a l l o w i n g m a n y t h o u s a n ds of f e e t of s e d i m e n t s to b e d e p o s i t e d . S i m i l a r c o n d i t i o n s p e r s i s t e d i n to P e r m i a n t i m e. No U p p e r P e r m i a n , T r i a s s i c , or J u r a s s i c r o c k s h a v e b e e n n o t e d in t h e S h e e p r o c k a r e a . L i m e s t o n e s c o n t a i n i n g L o w e r T r i a s s i c f a u n a h a ve b e e n found in t h e W a s a t c h R a n g e n e a r Salt L a k e C i t y , Utah, in the Ruby R a n g e , in e a s t - c e n t r a l N e v a d a , and at Gold H i l l , Utah (Nolan, 1 9 4 3 , p. 159). S i m i l a r l y , M e d : o c e r a s b e d s a r e p r e s e n t in t h e C o n f u s i o n Range In w e s t - c e n t r a l Utah ( Z e l l e r , 1951, p . 6 6 ) . This s u g g e s ts t h a t at l e a s t a L o w e r T r i a s s i c s e a o c c u p i e d the a r e a of w e s t - c e n t r al U t a h and p o s s i b l y c o v e r e d t h e S h e e p r o c k a r e a . Upper T r i a s s i c and J u r a s s i c r o c k s , though p r e s e n t n e a r Salt L a k e C i t y , Utah, h a v e not b e e n found In w e s t e r n Utah. 150 C R E T A C E O U S ( ? ) - T E R T I A R Y ( ? ) ROCKS G e n e r a l s t a t e m e nt R o c k s of an unknown but p o s t - P e n n s y l v a n i a n age a r e p r e s e n t in the n o r t h e r n p o r t i o n of t h e m a p p e d a r e a . The s t r a t a i n c l u d e b e d s of m a s s i v e r e d , m a r l y , f r i a b l e s i l t s t o n e o v e r l a i n by a h i g h l y s i i i c i f i ed c o n g l o m e r a t e ( P l a t e XXII), T h e s e r o c k s a r e p o o r l y e x p o s e d but p r o b a b l y e x c e e d 200 f e e t in t h i c k n e s s . The r e d , m a r l y u n i t l a p s on t h e s t e e p l y d i p p i n g O q u i r r h f o r m a t i o n , and t h e c o n g l o m e r a t e in t u rn o v e r l i e s the m a r l and o v e r l a p s the O q u i r r h . The s t r a t a of t h e y o u n g er s e q u e n c e dip f r o m 5 t o 15 d e g r e e s w e s t e r l y . P l a n t r e m a i n s a r e p r e s e n t in t h e c o n g l o m e r a t e a s a r e b o u l d e r s and c o b b l e s f r o m the O q u i r r h ( ? ) f o r m a t i o n ( P l a t e X X I I ) . Most of the c o b b l e s a re q u a r t z i t e ; v e r y f ew a r e l i m e s t o n e . The l i m e s t o n e c o b b l e s , which e s c a p e d s i l i c i f i c a t i o n , w e a t h e r out t o f o r m h o l e s a s do m a n y of t he t w i g s and s t e m s of t h e e n t o m b e d p l a n t s . Where t h e s t r a t a a r e weakly s i i i c i f i e d , the m a t e r i a l I s a p o o r l y s o r t e d c o n g l o m e r a t i c s a n d s t o n e. The s t r a t a a r e p o s t - t i l t i n g and m u s t , t h e r e f o r e , be c o n s i d e r e d y o u n g er t h a n l a t e C r e t a c e o u s. Figure I Looking north at the Tertiary conglomerate west of Lookout Pass. Figure 2 Closeup of the Tertiary conglomerate showing silicifieo' fragments of wood 151 T E R T I A R Y ROCKS G e n e r a l s t a t e m e nt S e v e r a l e x p o s u r e s of T e r t i a r y c o n g l o m e r a t e s w e r e n o t e d a l o ng t h e west f l a n k of t h e S h e e p r o c k M o u n t a i n s and in " L i t t l e V a l l e y ", which l i e s b e t w e e n t h e E a s t and W e s t L o o k o u t H i l l s . The c o n g l o m e r a t es a r e a l l y o u n g e r t h a n t h e n o r m a l f a u l t i n g , which f o r m e d the g r a b e n s t r u c t u r e o c c u p i e d by " L i t t l e V a l l e y " , and t h e m a t e r i a l c o m p r i s i n g the c o n g l o m e r a t e o r i g i n a t e d f r o m the s t r a t a of t h e u p t h r o w n b l o c k s . The p o s i t i o n of t h e c o n g l o m e r a t e r e l a t i v e to t h e f a u l t i n g s u g g e s t s a P l l o c e n e ( ? ) a g e . H i g h - l e v e l t e r r a c e s , though f a i n t , a r e p r e s e n t in " L i t t l e V a l l e y " and a r e c o n s i d e r e d to b e P l i o c e n e . S e v e r a l of the t e r r a c e s u r f a c e s a r e d e v e l o p e d on t h e c o n g l o m e r a t e s. T h e p e d i m e n t g r a v e l s a l o n g the f l a n k s of t h e r a n g e a r e of l a te T e r t i a r y a g e. 152 QUATERNARY G e n e r a l s t a t e m e nt At t h e m o u t h of N o r t h Oak B r u s h Canyon t h e r e i s a d e p o s i t of b o u l d e r y m a t e r i a l which m a y p o s s i b l y be a P l e i s t o c e n e t e r m i n al m o r a i n e . Some of t h e l a r g e b o u l d e r s a r e of the S h e e p r o c k s e r i es and h a v e b e e n t r a n s p o r t e d f r o m the h e a d of t h e c a n y o n , a d i s t a n ce of o v e r 3 m i l e s . Although the d e p o s i t m a y b e a m u d f l o w , the a b s e n c e of s p u r s and the r e a s o n a b l y w e l l - d e v e l o p e d U - s h a p e of N o r th Oak B r u s h C a n y o n lend s u p p o r t to t h e g l a c i a l o r i g i n of t h e d e p o s i t. B o n n e v i l l e l a k e b e d s c o v e r e d with r e c e n t a l l u v i a l m a t e r i a l a re p r e s e n t a l o n g t h e s o u t h w e s t and n o r t h w e s t p o r t i o n s of t h e m a p . R e c e n t m a t e r i a l c o m p r i s e s t a l u s c o n e s , f a n g l o m e r a t e m a t e r i a l, and s t r e a m s a n d s and g r a v e l. 153 IGNEOUS ROCKS G e n e r a l d i s t r i b u t i on I n t r u s i v e and e x t r u s i v e i g n e o u s r o c k s o c c u r in t h e S h e e p r o ck M o u n t a i n s a r e a . Both c r o p out o v e r n e a r l y e q u a l a r e a s and a r e c o n f i n e d to t h e s o u t h half of t h e a r e a . The i n t r u s i v e r o c k s a r e , in the m a i n , c o n f i n e d to the s o u t h f l a n k of t h e S h e e p r o c k R a n g e . A m o n z o n i te a n d a g r a n i t e s t o c k d o m i n a t e the i n t r u s i v e b o d i e s of q u a r t z d i o r i t e and s e e m to b e a s s o c i a t e d with t h e m o n z o n i t e s t o c k s . R h y o l i t i c and b a s ic d i k e s a r e a s s o c i a t e d with t h e s t o c k s . A b a s i c s i l l , p r o b a b l y P r e c a m b r i an i n a g e , i s a s s o c i a t e d with m e t a s e d i m e n t s of the S h e e p r o c k s e r i e s. E x t r u s i v e r o c k s a r e c h i e f l y of a n d e s i t i c and r h y o l i t i c c o m p o s i t i o n but i n c l u d e a s i n g l e m i n o r o c c u r r e n c e of b a s a l t . The e x t r u s i v e s a r e c o n f i n e d to a r e a s s o u t h and west of the i n t r u s i v e r o c k s. I n t r u s i v e r o c ks P r e c a m b r l a n ( ? j s i l l - A d i a b a s i c t e x t u r e d r o c k c r o p s out b e n e a th t h e Dutch P e a k t i l l i t e of t h e S h e e p r o c k s e r i e s in t h e v i c i n i t y of Dutch P e a k and e x t e n d s s o u t h e a s t to S e c . 28, T. 10 S . , R. 5 W. F l o a t f r om t h e s a m e r o c k t y p e was found on the west s i d e of P o l e C a n y o n , w h e r e the P r e c a m b r i a n s e c t i o n I s o v e r t u r n e d . The r o c k r a n g e s f r o m 60 to o v e r 100 f e e t in t h i c k n e s s . In t h e m a i n , I t s c o n t a c t s with t h e m e t a s e d i m e n t s a r e o b s c u r e , and t h e w r i t e r was not a b l e to a s c e r t a in w h e t h e r the m e t a m o r p h i s m i s c o n t a c t o r r e g i o n a l . The r o c k was 154 e x a m i n e d in t h i n s e c t i o n by B . J . S h a r p who r e p o r t s , " A n d e s i n e, g r u n e r i t e , c h l o r i t e , m a g n e t i t e p r e s e n t . Rock i s highLy a l t e r ed a n d p r o b a b l y a b a s i c siilV. T h e r o c k i s d e f i n i t e l y p r e - f o l d i n g and, t h e r e f o r e , p r e - T e r t i a r y. W e s t T i n t i c m o n z o n i t e s t o c k - The o l d e s t e x t e n s i v e i n t r u s i v e r o ck i n t h e e a s t e r n p a r t of t h e S h e e p r o c k M o u n t a i n s i s t h e W e s t T i n t i c s t o c k. L o u g h l i n (1920, p . 436) i d e n t i f i e d the r o c k a s a m o n z o n i t e and a s s i g n ed i t t o t h e T e r t i a r y . S t r i n g h a m (1942) m a p p e d the i n t r u s i v e in t h e West T i n t i c m i n i n g d i s t r i c t and v e r i f i e d L o u g h l i n ' s i d e n t i f i c a t i o n . The m o n z o n i t e c r o p s out in S e e s . 28, 29, 32 and 33, T . 11 S . , R. 5 W ., S a l t L a k e B a s e and M e r i d i a n , being a p p r o x i m a t e l y c i r c u l a r with a d i a m e t e r of about 6, 000 f e e t . It w e a t h e r s to f o r m r o u n d e d m a s s es a n d s u b d u e d t o p o g r a p h y . A s s o c i a t e d with t h e l a r g e r i n t r u s i v e a r e a s e r i e s of s m a l l e r s a t e l l i t i c b o d i e s which t r e n d n o r t h - n o r t h w e s t f r om t h e m o n z o n i t i c p a r e n t i n t r u s i o n to t h e d r a i n a g e of P o l e Canyon in S e c . 6, T. 11 S . , R. 5 W. L o u g h l i n (1920, p . 435) a n d S t r i n g h a m (1942, p p . 272-273) d e m o n s t r a t e t h a t P r e c a m b r i a n r o c k s h a v e b e e n t h r u s t o v e r P a l e o z o i c r o c k s in t h e West T i n t i c a r e a . F u r t h e r , they s h o w t h a t the m o n z o n i t e i n t r u s i o n i s p o s t - t h r u s t i n g , s i n c e it i n t r u d e s b o t h the u p p e r and l o w e r p l a t e s of t h e t h r u s t . G a r d n e r (1954) h a s d e t a i l ed t h e i n t r u s i v e r e l a t i o n s h i p s. 155 T h e n o r t h e r n and e a s t e r n e d g e s of t h e m o n z o n i t e * h e re i n t r u s i v e i n t o the P r e c a m b r i a n and P a l e o z o i c r o c k s , a r e e a s i ly t r a c e d b e c a u s e of t h e c o n t r a s t i n g l i t h o l o g i e s , a l t h o u g h t h e e x a ct c o n t a c t i s g e n e r a l l y c o n c e a l e d . The s o u t h w e s t and w e s t e r n l i m i t s of t he s t o c k a r e o b s c u r e d by p e d i m e n t g r a v e l s and a l l u v i u m . V o l c a n i c r o c ks a r e in f a u l t c o n t a c t with t h e m o n z o n i t e along i t s s o u t h e r n e x t r e m i t i e s. P e t r o g r a p h i c a l l y , the t y p i c a l m o n z o n i t e h a s a u n i f o r m , m e d i u m - g r a i n e d , g r a n i t i c t e x t u r e . S t r i n g h a m (1942, p . 274) s t a t e s: " W h i t e p l a g i o c l a s e , l i g h t - p i n k o r t h o c l a s e , b i o t i t e, a n d s m a l l c r y s t a l s of h o r n b l e n d e a r e d i s c e r n i b le i n h a n d s p e c i m e n . In a l l of s e v e r a l s p e c i m e n s s t u d i ed m i c r o s c o p i c a l l y it was found t h a t o r t h o c l a s e p r e d o m i n a t e s s l i g h t l y o v e r p l a g i o c l a s e , q u a r t z v a r i es f r o m 8 t o 17 p e r c e n t of t h e whole r o c k , and h o r n b l e n d e r e m a i n s c o n s t a n t at a r o u n d 5 to 6 p e r c e n t. M e d i u m - s i z e d p l a t e s of b i o t i t e c o n s t i t u t e 10 t o 12 p e r c e n t . Sphene, a u g i t e , m a g n e t i t e , and a p a t i te a r e t h e a c c e s s o r i e s . C h l o r i t e , m a g n e t i t e , s e r i c i t e, a n d e p i d o t e , p r e s e n t i n s p e c i m e n s i n m i n o r a m o u n t s, i n d i c a t e t h a t a l t e r a t i o n h a s b e e n s l i g h t . The t y p i c al t e x t u r e i s s e r i a t e with t h e l a r g e s t c r y s t a l s 3 t o 4 m m . i n g r e a t e s t d i m e n s i o n . . . ." T h e m o n z o n i t e i n t r u d e s P a l e o z o i c c a r b o n a t e s t r a t a , p r i n c i p a l ly of O r d o v i c i a n a g e , a l o n g i t s n o r t h e r n and e a s t e r n b o u n d a r i e s . A zone of c o n t a c t m e t a m o r p h i s m of c o n s i d e r a b l e width e x t e n d s a l o n g the e a s t e r n m a r g i n of t h e I n t r u s i o n . S t r i n g h a m (1942, p p . 277-278) r e p o r t s : " T h e c o n t a c t z o n e of t h e m o n z o n i t e a t t a i n s i ts g r e a t e s t width --=2, 5 0 0 f e e t - d i r e c t l y e a s t of the T i n t i c W e s t e r n m i n e (now D e s e r t T u n g s t e n ) and n a r r o w s t o w a r d the n o r t h and w e s t about 750 iL S B ';• o « Q Q 156 a l s o " N e a r the T i n t i c W e s t e r n m i n e , a l m o s t at t he c o n t a c t of t h e m o n z o n i t e , a c o a r s e l y c r y s t a l l i ne c a l c i t e m a r b l e h a s p r o m i n e n t l a m i n a t i o n s or s t r e a k s c o m p o s e d of b o t t l e - g r e e n i d o c r a s e a l t e r n a t i n g with white f l u o r e s c e n t w o l l a s t o n i t e. . o • U n d e r the m i c r o s c o p e b a n d s of q u a r t z, o r t h o c l a s e , and d i o p s i d e p a r a l l e l and a l t e r n a te w i t h t h e s e l a m i n a e . S c a t t e r e d t h r o u g h o u t the e n t i r e r o c k and i n c l u d e d in a l l m i n e r a l s a re s m a l l e p l d o t e c r y s t a l s , , " A n u m b e r of s m a l l e r i n t r u s i v e s a r e a s s o c i a t e d with t h e West T i n t i c s t o c k . Each i s r o u g h l y c i r c u l a r in a r e a and i n t r u d e s the P r e c a m b r i a n m e t a s e d i m e n t s . However, t h e i r c o n t a c t s a re o b s c u r e d e v e r y w h e r e by c o l l u v i um and s o i l . The s o u t h e r n m o s t of t h e m i n o r i n t r u s i v e m a s s e s in S e c . 17, T. 11 S . , R. 5 W. a re a p o r p h y r i t i c q u a r t z d l o r i t e . Thin s e c t i o n e x a m i n a t i o n r e v e a l ed t h e f o l l o w i n g : a n d e s i n e , 60 p e r c e n t ; q u a r t z , 20 p e r c e n t ; h o r n b l e n d e, 8 p e r c e n t ; b i o t i t e , 7 p e r c e n t ; o r t h o c l a s e , 5 p e r c e n t ; m a g n e t i t e , l e ss t h a n 1 p e r c e n t . A d i k e a s s o c i a t e d with t h i s i n t r u s i o n i s p r i n c i p a l ly h o r n b l e n d e and b i o t i t e and i s c l a s s i f i e d a s a s p e s s a r i t e . The n e xt i n t r u s i v e n o r t h of t h e q u a r t z d i o r l t e was found t o b e a g r a n i t e with a s i m i l a r s p e s s a r t l t e d i k e . The o t h e r i n t r u s i o n s f a r t h e r to t h e n o r th w e r e not i d e n t i f i e d by t h i n s e c t i o n , but in h a n d s p e c i m e n r e s e m b le t h e p a r e n t m o n z o n i t e. S h e e p r o c k g ^ Q ^ i t e _ s t o c k - The S h e e p r o c k g r a n i t e i s e x p o s ed o v e r an a r e a of a p p r o x i m a t e l y 9 s q u a r e m i l e s a l o n g t h e s o u t h s i d e of t h e r a n g e . It e x t e n d s a s a c o n c o r d a n t m a s s s o u t h e a s t e r l y f r o m the 157 h e a d of South Oak B r u s h C a n y o n to B u r n e d C a n y o n , a d i s t a n c e of n e a r l y 10 m i l e s . A p o p h y s e s of t h e g r a n i t e c r o p out In t h e b o t t om of J o e s C a n y o n and In A u t s C a n y o n . The m a i n s t o c k e x t e n d s 2 m i l e s f r o m the v a l l e y f l o o r to w i t h i n a m i l e of t h e d i v i d e. The g r a n i t e c l e a r l y i n t r u d e s o v e r t u r n e d and t h r u s t e d - P r e c a m b r i a n r o c k s in A u t s C a n y o n and J o e s Canyon and i s i n i n t r u s i ve c o n t a c t with O r d o v i c i a n r o c k s at i t s n o r t h w e s t e r n e x t r e m i t y. I t h a s b e e n d a t e d a s M i d d l e M i o c e n e (15 a n d 17 MY) by t h e U. S. G e o l o g i c a l S u r v e y ( p e r s o n a l c o m m u n i c a t i o n , H. T. M o r r i s ). W e a t h e r i n g h a s r e d u c e d t h e g r a n i t e to r o u n d e d c r u m b l y m a s s e s ; h o w e v e r , on the d i v i d e b e t w e e n H a r d - t o - B e a t and A l b e r t E k k e rs c a n y o n s , the g r a n i t e s t a n d s a s s p i r e s and o v e r h a n g i n g m a s s e s . S h e e t j o i n t i n g and t h e c o a r s e i n t e r l o c k i n g n a t u r e of t h e c o n s t i t u e nt m i n e r a l s a p p a r e n t l y c o n t r o l t h e c o n f i g u r a t i o n of t h e s e p e c u l i a r l a n d - f o r m s . Good h a n d s p e c i m e n s of f r e s h r o c k a r e r a r e . T h e m a i n g r a n i t e i s a l i m o n i t e - s t a i n e d , white to l i g h t g r ay r o c k with a m e d i u m to c o a r s e g r a n i t o i d t e x t u r e . Much of t h e r o ck i s p o r p h y r i t i c , e s p e c i a l l y n e a r t h e c o n t a c t with t h e P r e c a m b r i an m e t a s e d i m e n t s . O r t h o c l a s e p h e n o c r y s t s r a n g i n g f r o m one half to one and one half i n c h e s in d i a m e t e r a r e d i s t r i b u t e d u n i f o r m ly t h r o u g h o u t the r o c k . The g r o u n d m a s s i s p r i n c i p a l l y g r a y q u a r tz (45 p e r c e n t ) and m i c r o c l i n e (50 p e r c e n t ) with a l i t t l e b i o t i t e. 158 Two f a c i e s a r e r e c o g n i z e d i n t h e g r a n i t e : t h e c e n t r a l c o re i s w h i t e r ; w h e r e a s , the s u r r o u n d i n g r o c k i s m o r e l i m o n i t e - s t a i n e d and c a l l e d r e d f a c i e s in t h e f i e l d . T h e ' w h i t e ' f a c i e s is c o n s i d e r e d to b e a l a t e s t a g e d i f f e r e n t i a t e of t h e i n t r u s i v e. The ' w h i t e 9 f a c i e s c o n t a i n s b e r y l in p e g m a t i t i c f r a c t i o n s , in c l u s t e r s of r a d i a t i n g c r y s t a l s d i s s e m i n a t e d t h r o u g h o u t t h e r o c k , ( P l a t e XXIII) a s d i s p e r s e d g r a n u l e s , and in t h i n v e i n l e t s . The "white1 ' f a c i e s is c e n t e r e d in H a r d - t o - B e a t Canyon and c r o p s out o v e r an a r e a of a p p r o x i m a t e l y 1 s q u a r e m i l e. T h e m a i n m a s s of g r a n i t e i s c u t b y n u m e r o u s s e t s of j o i n t s. The s t r o n g e s t s e t s t r i k e s n o r t h e a s t and d i p s n e a r l y v e r t i c a l . A m i n or s e t t r e n d s n o r t h w e s t and d i p s at a s h a l l o w a n g l e . The j o i n t s c o n t a in i i m o n i t e which l o c a l l y g i v e s t h e r o c k a r e d - b r o w n t i n t. A p l i t e d i k e s a n d g r e l s s e n i z e d f r a c t u r e z o n e s cu t t h e g r a n i te i n n o r t h e a s t e r l y d i r e c t i o n s . T u n g s t e n m i n e r a l s , p r i n c i p a l ly w o l f r a m i t e and s o m e h u b n e r i t e , a r e a s s o c i a t e d with s o m e of the g r e i a s e n z o n e s . The p e g m a t i t i c p o d s o c c u r r i n g in t h e g r a n i t e a re g e n e r a l l y d e v o i d of v a l u a b l e m i n e r a l s ; h o w e v e r , s a m a r s k i t e and b e r y l h a v e b e e n r e c o v e r e d f r o m s o m e. A r h y o l i t e d i k e , r a n g i n g in width f r o m a f ew f e e t to n e a r l y 50 f e e t , c u t s t h e g r a n i t e a l o n g i t s s o u t h w e s t e r n m a r g i n f r o m the m o u t h of B u r n e d Canyon n o r t h w e s t e r l y to t h e d r a i n a g e of A l b e rt E k k e r s C a n y o n . The d i k e i s t r a c e d by f l o a t and in p l a c e s by the 159 p r e s e n c e of m o r e p r o l i f i c v e g e t a t i o n . The r o c k i s d e n s e with p h e n o c r y s t s of q u a r t z , o r t h o c l a s e , and o l i g o c i a s e , r a n g i n g f r om 2 m m . to 5 m m . in d i a m e t e r , in a f i n e g r o u n d m a s s of o r t h o c l a se a n d q u a r t z with s o m e m a g n e t i t e . The d i k e and an a s s o c i a t e d c o p p e r - f l u o r i t e v e i n s y s t e m a r e b o t h a p p r o x i m a t e l y p a r a l l e l t o t h e s o u th f l a n k f a u l t . The d i k e and t h e v e i n s y s t e m m a y be c l o s e l y a s s o c i a t ed i n a g e s i n c e b o t h a r e m o r e r a d i o a c t i v e t h a n t h e i n t r u d e d g r a n i t e. E x c e p t f o r m i n o r a m o u n t s of p y r i t e in t h i n f r a c t u r e s in t h e d i k e n e ar B u r n e d C a n y o n , no m i n e r a l i z a t i o n of t h e d i k e was o b s e r v e d. A t h i c k p r o m i n e n c e of a n d e s i t e i s p r e s e n t n e a r t h e p e r e n n i al s p r i n g in E l d e r b e r r y Canyon on t h e w e s t f l a n k of t h e r a n g e . The h e i g h t and p o s i t i o n of t h i s m a s s i n d i c a t e t h a t it m a y b e a r e m n a nt of a s h o r t c h a i n of s m a l l v o l c a n o e s a l i g n e d a l o n g t h e west f l a n k f a u l t. E x t r u s i v e r o c ks G e n e r a l s t a t e m e n t - The f l o w s a l o n g t h e s o u t h and w e s t f l a n ks of the S h e e p r o c k M o u n t a i n s a r e m a i n l y a n d e s i t i c in c o m p o s i t i o n and a r e p r o b a b l y c l o s e l y a s s o c i a t e d with t h e f l a n k i n g n o r m a l f a u l t s and a r e p r o b a b l e l a t e M i o c e n e o r P l i o c e n e . The i g n e o u s r o c k s a r o u nd t h e A l l i s o n K n o l l s a r e p a r t of an i n t r u s i v e and v o l c a n i c c e n t er l o c a t e d in t h e D e s e r t M o u n t a i n s . The s i m i l a r i t y b e t w e e n the D e s e r t M o u n t a i n s i n t r u s i v e and t h e S h e e p r o c k s t o c k s u g g e s t s t h at t h i s a s s e m b l a g e i s M i o c e n e in a g e a l s o . The only b a s a l t f l ow i s in t h e S i m p s o n M o u n t a i n s r e g i o n , s o u t h of B l a c k ' s R a n c h . It is 160 t h o u g h t to b e t h e y o u n g e s t e x t r u s i v e r o c k in the a r e a m a p p e d. E x t r u s i v e s in t h e W e s t T i n t i c a r e a - The W e s t T i n t i c m o n z o n i te s t o c k i s i n f a u l t c o n t a c t with v o l c a n i c r o c k s of a n d e s i t i c c o m p o s i t i on a l o n g i t s s o u t h e r n b o r d e r . The a n d e s i t e s and s o m e a s s o c i a t e d tuffs a p p e a r to b e r e l a t i v e l y f l a t - l y i n g and a r e p r o b a b l y l a t e M i o c e n e or P l i o c e n e in a g e . The v o l c a n i c s a r e of c o n s i d e r a b l e t h i c k n e s s n e ar t h e c o n t a c t . D r i l l i n g in t h e a r e a r e v e a l e d b e t w e e n 400 a n d 800 f e e t of v o l c a n i c s o v e r l y i n g the m o n z o n i t e. E x t r u s i v e s f l a n k i n g t h e S h e e p r o c k s t o c k - The r h y o l i t i c e x t r u s i ve on the west s i d e of South P i n e C a n y o n o c c u p i e s t h e a r e a of a s m a ll d r a i n a g e b a s i n . The p o s i t i o n and f l ow b a n d i n g of t h i s r o c k i n d i c a te t h a t it f l o w e d s o u t h e r l y o v e r a r e l a t i v e l y m a t u r e d i s s e c t e d e r o s i on s u r f a c e . Since no f a u l t s a r e l o c a t e d n o r t h of t h e v o l c a n i c o c c u r r e n c e, i t m a y be a s s u m e d that t h e S h e e p r o c k g r a n i t e in t h a t a r e a i s m o st l i k e l y of l a t e M i o c e n e o r P l i o c e n e a g e . The a n d e s i t i c o c c u r r e n ce i n the E l d e r b e r r y Canyon a r e a l i k e w i s e i s a s s o c i a t e d with f l a n k i ng f a u l t s , a n d p a r t s of it h a v e b e e n b e v e l e d by t h e h i g h l e v e l M i o c e n e - P l i o c e n e e r o s i o n s u r f a c e which s l o p e s w e s t w a r d t o w a r d E r i c k s o n 's P a s s . E x t r u s i v e s f l a n k i n g the S i m p s o n M o u n t a i n s - V o l c a n i c r o c ks of r h y o l i t i c and a n d e s i t i c c o m p o s i t i o n and l ow e a s t e r l y d i p f l a nk t h e S i m p s o n M o u n t a i n s . The v o l c a n i c s a r e , in t h e m a i n , not a f f e c t e d by t h e n u m e r o u s g r a v i t y f a u l t s which c u t t h e P a l e o z o i c r o c ks 161 i n t h a t a r e a . The v o i c a n i s m i s p r o b a b l y l a t e M i o c e n e and P l i o c e ne i n a g e . The e x t r u s i v e s h a v e b e e n t r u n c a t e d by l o w - l e v e l P l i o c e ne p e d i m e n t s u r f a c e s in the v i c i n i t y of E r i c k s o n P a s s . A n i m a l b u r r o w s in t h e O r d o v i c i a n s h a l e s p e n e t r a t e v o l c a n ic r o c k , i n d i c a t i n g t h a t f e e d e r s f o r the r h y o l i t e a r e p r e s e n t a l o n g the w e s t f l a n k of t h e S i m p s o n M o u n t a i n s . A s m a l l b a s a l t f l ow c o v e r i ng s e v e r a l a c r e s i s p r e s e n t in t h e a r e a . It i s o n l y a f ew y a r d s t h i ck a n d d i p s with t h e e r o s i o n s u r f a c e . This b a s a l t m a y b e a s young a s P l e i s t o c e n e and m a y c o i n c i d e in a g e with t h e b a s a l t i c f i e l d s to t h e s o u t h ( n o r t h w e s t of D e l t a , U t a h ). V o l c a n i c s in A l l i s o n K n o l l s - Volcanic b r e c c i a s and r h y o l i t ic and a n d e s i t i c f l o w s , t o g e t h e r with a p r o b a b l e v o l c a n i c p l u g , a re p r e s e n t in t h e A l l i s o n K n o l l s . The v o l c a n i c s i n t r u d e and c o v er P r e c a m b r i a n and O r d o v i c i a n r o c k s which w e r e i n v o l v e d in t h r u s t i ng i n t h e a r e a . The v o l c a n i c s a r e a p p r o x i m a t e l y t h e s a m e age a s t h o se f l a n k i n g t h e S h e e p r o c k R a n g e ( M i o c e n e - P l i o c e n e ). 162 S T R U C T U R E M a j o r f e a t u r es T h e s t r u c t u r a l e l e m e n t s of t h e S h e e p r o c k a r e a c o n s i s t of a n o r t h - d i p p i n g m o n o c l i n e , n o r t h - t r e n d i n g f o l d s , n o r t h - t r e n d i ng l o w - a n g l e t h r u s t s , o l d e r h i g h - a n g l e f a u l t s , l o w - a n g l e s t r i k e - s l ip f a u l t s , and e a s t - t r e n d i n g t h r u s t s . The s t r u c t u r e s in above s e q u e n c e a r e t h e r e s u l t of p r o g r e s s i v e s t a g e s of d e f o r m a t i on d u r i n g t h e L a r a m i d e o r o g e n y . A n u m b e r of l e s s p r o m i n e n t , h i g h - a n g l e n o r m a l a n d s t r i k e - s l i p f a u l t s r a n g e f r o m L a r a m i d e to R e c e n t. F o l d s S h e e p r o c k m o n o c l i n e - The S h e e p r o c k m o n o c l i n e i s t h e d o m i n a nt s t r u c t u r a l e l e m e n t in the S h e e p r o c k M o u n t a i n s . It e x t e n d s f r o m the g r a n i t e c o n t a c t n o r t h w a r d to L o o k o u t P a s s , and f r o m V e r n o n C r e ek on t h e e a s t to Skull V a l l e y on t h e w e s t . Rocks r a n g i n g in a g e f r om P r e c a m b r i a n t h r o u g h M i s s i s s i p p i a n a r e i n v o l v e d in t h e s t r u c t u re which d i p s f r o m 35 d e g r e e s to 55 d e g r e e s to t h e n o r t h and n o r t h e a s t. The o r i e n t a t i o n of t h e S h e e p r o c k m o n o c l i n e i s e a s t - w e s t which is c o n t r a r y to t h e n o r t h - s o u t h f o l d i n g p r e s e n t in t h e n o r t h - l y i n g Onaqui a n d S t a n s b u r y r a n g e s. P o l e C a n y o n a n t i c l i n e - A m a j o r n o r t h - t r e n d i n g r e c u m b e n t l i mb of an a n t i c l i n e i s e v i d e n t f r o m the a r e a l d i s t r i b u t i o n of P r e c a m b r i an r o c k s in the v i c i n i t y of P o l e C a n y o n s o u t h of t h e d i v i d e . The f o i d , h e re r e f e r r e d to a s t h e P o l e Canyon a n t i c l i n e , e x t e n d s f r o m J o e s Canyon 163 e a s t w a r d to t h e h e a d of Cow H o l l o w . It i s t e r m i n a t e d on t h e n o r th by t h e P o l e Canyon f a u l t , on t h e e a s t by a L a r a m i d e f a u l t c o m p l ex ( e a s t of m a p p e d a r e a ) , on t h e s o u t h by a c o v e r of p e d i m e n t g r a v el a n d c o l l u v i u m , and on t h e w e s t by t h e S h e e p r o c k g r a n i t e . The e x a ct p o s i t i o n of t h e a n t i c l i n a l a x i s i s u n c e r t a i n . The S h e e p r o c k o r r e l a t ed t h r u s t s w e r e p r o b a b l y c o n t e m p o r a r y s t r u c t u r e s . The P o l e Canyon a n t i c l i n e was t o r n , t h r u s t , and d r a g g e d to i t s p r e s e n t p o s i t i o n by L a r a m i d e f o r c e s . The e x p o s e d r o c k s of t h e s t r u c t u r e a r e m o s t ly n e a r v e r t i c a l . They a r e s l i g h t l y o v e r t u r n e d n e a r t h e g r a n i t e c o n t a c t, a n d t h e d e g r e e of o v e r t u r n i n g i n c r e a s e s e a s t e r l y to a m a x i m u m of 15 t o 20 d e g r e e s and d i p s w e s t w a r d in t h e v i c i n i t y of Cow H o l l o w . The r o c k s e a s t of C o w H o l l ow a r e p o o r l y e x p o s e d , b u t a f ew e x p o s u r es e a s t of t h e m a p b o u n d a r y i n d i c a t e t h a t t h e o v e r t u r n e d l i m b h a s b e en t h r u s t e a s t e r l y and t h a t the t h r u s t s u r f a c e m a y be the S h e e p r o ck t h r u s t o r one which i s c l o s e l y r e l a t e d to t h e m a j o r t h r u s t i n g in the a r e a. D e a t h C a n y o n ^ a n t i c l i n e «=* T h e m a j o r s t r u c t u r e p r e s e n t in the s o u t h e r n p o r t i o n of t h e S i m p s o n M o u n t a i n s i s t h e n o r t h - p l u n g i ng D e a t h C a n y o n a n t i c l i n e . The a n t i c l i n e I s s y m m e t r i c a l with an a x is t h a t t r e n d s a p p r o x i m a t e l y n o r t h and c o i n c i d e s with t h e d r a i n a g e of D e a t h C a n y o n . The e a s t e r n l i m b of t h e a n t i c l i n e i s i n c l u d e d in the m a p p e d a r e a . As f a r a s i s known, r o c k s r a n g i n g in a g e f r o m P r e c a m b r i a n t h r o u g h b a s a l C a m b r i a n q u a r t z i t e s a r e p r e s e n t in t h is 164 s t r u c t u r e . Dips r a n g i n g f r o m 40 to 60 d e g r e e s to t h e n o r t h e a s t a re p r e s e n t a l o n g t h e e a s t e r n l i m b . The a n t i c l i n e i s t e r m i n a t e d on the n o r t h , in t h e v i c i n i t y of B l a c k ' s R a n c h , by a l a r g e e a s t - w e s t f a u lt which e x t e n d s t h r o u g h t h e S i m p s o n R a n g e . This f a u l t i s e i t h e r a g r a v i t y o r a s t r i k e - s l i p f a u l t . The n o s e of t h e D e a t h C a n y o n a n t i c l i n e i s b e l i e v e d to b e c o v e r e d by a l l o c h t h o n o u s b l o c k s of s u b s e q u e nt t h r u s t s . Younger n o r m a l f a u l t i n g f u r t h e r c o m p l i c a t e s the s t r u c t u r al i n t e r p r e t a t i o n in t h e S i m p s o n M o u n t a i n s. F a u l t s S h e e p r o c k t h r u s t - The S h e e p r o c k t h r u s t ( L o u g h l i n , 1920, p. 436) w a s f i r s t r e c o g n i z e d in t h e W e s t T i n t i c m i n i n g d i s t r i c t n e a r the s o u t h e a s t end of t h e S h e e p r o c k M o u n t a i n s . Subsequent w o r k e rs ( S t r i n g h a m , 1942; G a r d n e r , 1954) h a v e c o n f i r m e d the p r e s e n c e of t h e t h r u s t and h a v e a d d e d s o m e d e t a i l to i t s o u t l i n e . The S h e e p r o ck t h r u s t i n v o l v e s t h r u s t i n g of P r e c a m b r i a n r o c k s ( I n c l u d i n g t i l l i t e) o v e r r o c k s r a n g i n g f r o m C a m b r i a n ( ? ) to D e v o n i a n in a g e . Rocks of u p p e r P a l e o z o i c age m a y h a v e b e e n o v e r t h r u s t f a r t h e r to t h e e a s t, a n d a s u b s e q u e n t work by S i d n e y Groff will p r o b a b l y d e l i n e a t e the r e l a t i o n s h i p s of t h e S h e e p r o c k t h r u s t i n t h e e a s t - l y i n g W e s t T i n t ic M o u n t a i n s . The S h e e p r o c k t h r u s t c a n be t r a c e d only by t h e p r e s e n ce of windows of P a l e o z o i c c a r b o n a t e r o c k s in t h e u p p e r p l a t e . The l a r g e s t e x p o s u r e i s n e a r t h e W e s t T i n t i c m o n z o n i t e In S e c . 28, T. I I S . , R. 5 W. Another s m a l l e x p o s u r e I s i n I n d i a n Hollow 165 a p p r o x i m a t e l y one and one half m i l e s n o r t h w e s t of t h e m a i n m a s s of t h e W e s t T i n t i c m o n z o n i t e . The t h r u s t p l a n e r a n g e s in d i p f r o m n e a r - h o r i z o n t a l to 15 d e g r e e s n o r t h w a r d . The W e s t T i n t i c m o n z o n i t e h as p e n e t r a t e d b o t h t h e l o w e r and u p p e r p l a t e s of t h e t h r u s t and t h e a t t e n d e nt m e t a m o r p h i s m h a s o b l i t e r a t e d p r i m a r y s t r u c t u r e s of m a n y of the c a r b o n a t e r o c k s of t h e w e s t e r n m o s t r o c k s of the w i n d o w s . Rocks i n v o l v e d in t h r u s t i n g 9 p r o b a b l y r e l a t e d t o t h e S h e e p r o c k t h r u s t , c r o p out i n t h e A l l i s o n K n o l l s n e a r t h e c e n t e r of t h e s o u t h e d g e of t h e m a p p ed a r e a . Dark b l u e - g r a y d o l o m i t e s e x p o s e d on t h e e a s t e r n s i d e of A l l i s o n K n o l l s a r e i n n e a r l y h o r i z o n t a l c o n t a c t with t h e u n d e r l y i ng P r e c a m b r i a n t i l i i t e s . The d o l o m i t e s a r e a s s i g n e d to t h e O r d o v i c i an on t h e b a s i s of c o l o r and t h e p r e s e n c e of H a l y s i t e s , and a r e t h o u g h t to b e u n i t s of t h e F i s h H a v e n d o l o m i t e . The c a r b o n a t e s dip 41 d e g r e es n o r t h e a s t , w h e r e a s t h e u n d e r l y i n g t i l l i t e s d i p f r o m 35 to 48 d e g r e es i n t h e s a m e d i r e c t i o n. I n t h e n o r t h e r n p a r t of t h e West L o o k o u t H i l l s , a i l o c h t h o n o us b l o c k s of q u a r t z i t e a n d s i l i c i f i e d l i m e s t o n e , b e a r i n g c r i n o i d c o i u m n a l s, h a v e b e e n t h r u s t o v e r r o c k s which r a n g e f r o m O r d o v i c i a n to M i s s i s s i p p i a n in a g e . T h e s e o v e r t h r u s t s e d i m e n t s a r e t e n t a t i v e ly i d e n t i f i e d a s O q u i r r h f o r m a t i o n of P e n n s y l v a n i a n a g e . The d i p of the s t r a t a of b o t h t h e t h r u s t p l a t e s i s a p p r o x i m a t e l y 45 d e g r e es n o r t h e r l y . The f a u l t s u r f a c e i s s o m e w h a t u n d u l a t o r y , as s u g g e s t ed by t h e s l i g h t d i f f e r e n c e s in e l e v a t i o n of t h e b a s e s of t h e a i l o c h t h o n o us 166 b l o c k s which o c c u p y the c r e s t s of t h e h i l l s i n t h e a r e a c This t h r u st i s r e l a t e d to t h e m o v e m e n t which p r o d u c e d t h e S h e t p r o e k t h r u s t and t h e n o r t h - s o u t h f o l d s of t h e n o r t h = l y i m g O n a q u i and S t a n s b u r y Moun-t a i n s 0 The t h r u s t i n g in the L o o k o u t H i l l s p r o b a b l y i s an e x t e n s i on of t h e L o s R i c o s t h r u s t of C r o f t ( 1 9 5 6 9 p c 29) which i s e x p o s e d along t h e w e s t f l a n k of t h e Onaqui M o u n t a i n s* T h e h i g h e s t e l e v a t i o n in t h e we s t r i v i n g S i m p s o n M o u n t a i n s a re a i l o c h t h o n o u s b l o c k s of P r e c a m b r i a n q u a r t z i t e , and a r e m o s t l i k e ly r e l a t e d to t h e S h e e p r o c k t h r u s t . Although t h e a r e a i s h i g h l y d i s t u r b ed by n o r m a l f a u l t i n g , the p r e s e n c e of P r e c a m b r i a n s t r a t a in t h e h i g h er e l e v a t i o n s s u g g e s t s t h a t b o t h t h e P r e c a m b r i a n and m u c h of t h e C a m b r i an s e d i m e n t s h a v e b e e n t h r u s t to t h e i r p r e s e n t p o s i t i o n * Without t h r u s t~ i n g , n o r m a l f a u l t s with r e l a t i v e d i s p l a c e m e n t s of" a b o u t 109 000 f e et would b e n e c e s s a r y t o a c c o u n t f o r t h e o u t c r o p p a t t e r n , and s o m e of t h e s e would b e only a f ew h u n d r e d f e e t a p a r t c O l d e r n o r m a l f a u l t s ° The p r i n c i p a l s o l d e r , h i g h - a n g l e f a u l ts a r e c o n f i n e d to t h e west f l a n k of t h e S h e e p r o c k R a n g e G They a re m o s t p r o n o u n c e d at t h e i r s o u t h e r n e x t r e m i t i e s west of B e n n i o n and T a l a w a g P e a k s „ The f a u l t s s t r i k e n o r t h = s o u t h and d i p f r o m v e r t i c al t o s l i g h t l y westo L a t e r m o v e m e n t s a l o n g t h e w e s t f l a n k f a u l t h a ve a c c e n t u a t e d i t s s c a r p 0 The p r e s e n c e of t h e m o n o c l i n a l s t r u c t u re i n d i c a t e s t h a t t h e i n i t i a l m o v e m e n t a l o n g t h e f a u l t m a y h a v e b e en e s s e n t i a l l y a d i a g o n a l f a u l t f s t r i k e ° s l i p f a u l t with r e l a t i v e m o v e m e nt 167 of e a s t e r n b l o c k r i s i n g a s i t m o v e d in a. s o u t h e r l y d i r e c t i o n ) . The c o v e r e d a r e a a l o n g t h e w e s t s i d e of t h e r a n g e o b s c u r e s t h e b a s e m e nt r o c k s which a r e n e c e s s a r y to e s t a b l i s h t h e e x a c t r e l a t i o n s h i p of t h e f a u l t . Rocks r a n g i n g in a g e f r o m C a m b r i a n to D e v o n i a n a re p r e s e n t on t h e d o w n t h r o w n s i d e of t h e f a u l t . The d i f f e r e n c e s b e t w e en d i p of t h e s t r a t a in t h e S i m p s o n M o u n t a i n s and t h e S h e e p r o c k m o n o c l i ne i n d i c a t e t h a t t h e w e s t f l a n k f a u l t i s c l o s e l y r e l a t e d to t h e f o r m a t i o n of t h e S h e e p r o c k m o n o c l i n e. A n o t h e r h i g h - a n g l e f a u l t , t r e n d i n g n e a r l y e a s t - w e s t , t r a n s v e r s e to t h e a x i s of t h e s o u t h e r n O n a q u i M o u n t a i n s i s h e r e c a l l e d t h e Onaqui f a u l t . This f e a t u r e m a r k s the j u n c t i o n of t h e n o r t h - s o u t h f o l d s y s t em on t h e O n a q u i M o u n t a i n s with t h e n o r t h w a r d - d i p p i n g s t r a t a c o m p r i s i ng t h e S h e e p r o c k m o n o c l i n e . The O n a q u i f a u l t i s c o n c e a l e d b e n e a th a l l u v i um b o t h e a s t and w e s t of t h e r a n g e . Johnson (1956, F i g u r e 2), i n t e r p r e t i n g g r a v i t y m e a s u r e m e n t s at t h e s o u t h end of S k u l l V a l l e y, i n d i c a t e s an a n o m a l o u s c o n d i t i o n e a s t of D a v i s M o u n t a i n which m ay b e c a u s e d by t h e p r e s e n c e of t h e B u r i e d O n a q u i f a u l t. P o l e C a n y o n t h r u s t - A m a j o r , n o r t h - d i p p i n g , h i g h - a n g l e t h r u st e x p o s e d a l o n g t h e h e a d s of P o l e and A u t s C a n y o n s i s h e r e r e f e r r e d to a s t h e P o l e C a n y o n t h r u s t ( P l a t e XXIV, F i g u r e 2). D i s p l a c e m e nt a l o n g it i s to t h e s o u t h and s o u t h w e s t . The t h r u s t t r a c e c a n be f o l l o w e d f r o m the d i v i d e n e a r the h e a d of Cow H o l l ow w e s t w a r d t h r o u gh t h e h e a d s of P o l e and A u t s C a n y o n s , t h e n c e n o r t h w e s t i n t o B e n n i on PLATE Figure I View to the north of Lion Hill. Segments of the Lion Hill thrust are marked on the photograph. Lighter Tintic quartzite in center foreground is thrust over the Precambrian. Middle Cambrian carbonates comprising the upper part of the hill are thrust over the Tintic quartzite. Figure 2 View to the northwest near Bennion Canyon showing limonite-stained thrust plate. The rocks in the lower right and the rocks in the ridge in the background are thrust to the south. 168 C a n y o n , t h e n c e s o u t h t o t h e S h e e p r o c k g r a n i t e . The S h e e p r o ck g r a n i t e i s l a t e r t h a n the t h r u s t a n d p r o b a b l y i n t r u d e s t h e a r e a c o n t a i n i n g t h e w e s t w a r d t r a c e of t h e t h r u s t . The P o l e C a n y o n t h r u st i s of unknown but p r o b a b l y s e v e r a l m i l e s d i s p l a c e m e n t . The d r ag a n d c o m p r e s s i o n a l f o l d s o b s e r v e d a l o n g t h e t h r u s t p l a n e i n d i c a te m o v e m e n t f r o m the n o r t h and n o r t h e a s t . P r e c a m b r i a n r o c k s of the o v e r t u r n e d P o l e Canyon a n t i c l i n e a r e t r u n c a t e d and o v e r r i d d e n - b y the P r e c a m b r i a n r o c k s of t h e u p p e r p l a t e . The t h r u s t i n v o l v e d a l l t h e s t r a ta of t h e h i g h e s t p o r t i o n s of t h e r a n g e . The d i p of t h e t h r u s t p l a n e r a n g es f r o m 45 t o 65 d e g r e e s n o r t h e r l y. L i o n H i l l and r e l a t e d n o r t h f l a n k t h r u s t s - The L i o n H i l l and r e l a t ed t h r u s t s a r e c o n f i n e d to t h e a r e a n o r t h of t h e S h e e p r o c k d r a i n a g e d i v i d e. T h e o u t c r o p of t h e t h r u s t c a n be t r a c e d a r o u n d L i o n H i l l and i n t o the f o o t h i l l s e a s t a n d w e s t of t h e m o u t h of H a r k e r C a n y o n ( P l a t e XXIV, F i g u r e 1). A s m a l l e r p a t c h of w h i t e q u a r t z i t e l o c a t e d n o r t h of L i t t le V a l l e y i s in t h r u s t c o n t a c t with u n d e r l y i n g P r e c a m b r i a n r o c k s . The t h r u s t s a r e l o w - a n g l e ; t h e y d i p 10 t o 15 d e g r e e s n o r t h e r l y . Rocks of t h e C a m b r i a n s y s t e m , r a n g i n g f r o m the T i n t i c q u a r t z i t e to t h e M a r j um f o r m a t i o n , have b e e n t h r u s t o v e r P r e c a m b r i a n s t r a t a a s s i g n e d to t he M u t u a l f ? ) f o r m a t i o n and p a r t of t h e u p p e r S h e e p r o c k s e r i e s . The s t r a t i g r a p h i c d i s p l a c e m e n t i s a p p r o x i m a t e l y one m i l e * The d i p s of the s t r a t a of t h e u p p e r p l a t e of t h e t h r u s t m o r e o r l e s s c o i n c i d e with t he d i p of the r o c k s of t h e l o w e r p l a t e which a r e d i s p o s e d 45 d e g r e es 169 n o r t h e a s t w a r d . The s i m i l a r i t y of t h e C a m b r i a n s t r a t a of t h e t h r u st s e g m e n t with t h e s u r r o u n d i n g C a m b r i a n s e c t i o n s p r e c l u d e s the p o s s i b i l i t y t h a t t h i s , the L i o n H i l l , t h r u s t c o m p r i s e s r o c k s f ar r e m o v e d f r o m the C a m b r i a n s e c t i o n s in t h e v i c i n i t y ; t h e r e f o r e , it i s c o n c l u d e d t h a t t h e s t r a t a r e c o g n i z e d in t h e u p p e r p l a t e h a v e not b e e n d i s p l a c e d any g r e a t d i s t a n c e and t h a t the o u t c r o p p a t t e r n of t he a r e a i n d i c a t e s t h a t t h e m o v e m e n t on t h e t h r u s t i s to t h e s o u t h and s o u t h w e s t . F u r t h e r , the d i p of t h e t h r u s t p l a n e i n d i c a t e s t h a t t he c o m p r e s s i o n p r o d u c i n g t h e t h r u s t was p o s t - t i l t i n g of t h e S h e e p r o ck m o n o c l i n e . L o w - a n g l e , s t r i p e - s l i p f a u l t s - An e a s t - w e s t , n o r t h - d i p p i n g, s t r i k e - s l i p f a u l t i s t r a c e a b l e a c r o s s t h e r a n g e in t h e v i c i n i t y of E a st a n d W e s t G o v e r n m e n t C a n y o n s . This f a u l t i s r e f e r r e d to a s t he G o v e r n m e n t C r e e k f a u l t . The f a u l t p l a n e d i p s n o r t h f r o m 30 t o 45 d e g r e e s . S t r a t a of t h e u p p e r S h e e p r o c k s e r i e s h a v e b e e n m o v e d o v er s t r a t a of t h e M a r j u m f o r m a t i o n , a s t r a t i g r a p h i c d i s t a n c e of a p p r o x i m a t e l y 5 , 0 0 0 f e e t . The r e l a t i v e m o v e m e n t of t h e h a n g i n g wall b l o ck a p p e a r s to b e w e s t w a r d and s o u t h . The g r e a t e r c o m p o n e n t i s w e s t e r ly a n d p r o b a b l y did n o t e x c e e d 4 m i l e s . This f a u l t i s p r o b a b l y a s s o c i a t ed wit h t h e f o r c e s which p r o d u c e d t h e P o l e Canyon and L i o n H i l l t h r u s t s. O t h e r s t r i k e - s l i p f a u l t s of l e s s e r d i s p l a c e m e n t t h a n t h e G o v e r n m e nt C r e e k f a u l t a r e the Red P i n e C r e e k and t h e L o o k o u t P a s s f a u l t s . The Red P i n e C r e e k f a u l t l o c a t e d n o r t h of L o o k o u t P e a k (Red P i n e M o u n t a i n) d i p s n o r t h 18 d e g r e e s . The f a u l t i s d i f f i c u l t to t r a c e but a b s e n ce 170 of n o r m a l s t r a t i g r a p h i e u n i t s i n d i c a t e s t h a t t h e n o r t h - l y i ng h a n g i n g wall b l o c k c u t out b e t w e e n 600 and 1, 000 f e e t of s t r a t a. T h e r e l a t i v e m o v e m e n t on t h i s f a u l t i s d i f f i c u l t to d e t e r m i n e but i s p r e s u m e d to f a v o r a w e s t w a r d m o v e m e n t f o r t h e h a n g i n g wall b l o c k . The h i g h - a n g l e , n o r t h e a s t - t r e n d i n g s t r i k e - s l i p f a u l t s in the W e s t L o o k o u t H i l l s l y i n g b e t w e e n the L o o k o u t P e a k and L o o k o u t P a ss v e r i f y t h i s i n t e r p r e t a t i o n. T h e L o o k o u t P a s s f a u l t i s t r a c e d f o r only a s h o r t d i s t a n c e in a n o r t h w e s t d i r e c t i o n n o r t h of t h e L o o k o u t P a s s r o a d . W e s t w a r d , the f a u l t i s o b s c u r e d by fan g r a v e l s . The C h i u l o s s h a l e m e m b e r of the G r e a t B l u e f o r m a t i o n i s c u t out by t h e f a u l t i n g e a s t of L o o k o u t P a s s . R e l a t i v e m o v e m e n t of t h e h a n g i n g wall b l o c k to t h e west p l a c e s the u p p e r G r e a t B l u e l i m e s t o n e m e m b e r in c o n t a c t with t h e l o w e r l i m e s t o n e m e m b e r . The m i s s i n g i n t e r v a l r e p r e s e n t s a p p r o x i m a t e l y 2, 000 f e e t of s t r a t a , the e n t i r e C h i u l o s m e m b e r . A s m a l l s y n c l i n e is d e v e l o p e d in t h e f o o t w a l l b l o c k e a s t of t h e p a s s which i n d i c a t e s an e a s t w a r d m o v e m e n t f o r t h a t s e g m e n t. M i o c e n e n o r m a l f a u l t i n g - The n o r m a l f a u l t i n g a s s o c i a t e d with t h e i n t r u s i o n of t h e S h e e p r o c k g r a n i t e i s M i o c e n e in a g e . The t r e nd of t h e f a u l t s i s g e n e r a l l y at r i g h t a n g l e s to t h e i n t r u s i v e c o n t a c t and of s m a l l d i s p l a c e m e n t s . The m a j o r f a u l t a l o n g t h e e a s t s i d e of the S i m p s o n M o u n t a i n s was e i t h e r i n i t i a t e d o r r e j u v e n a t e d at t h i s t i me a s was t h e west f l a n k f a u l t along t h e S h e e p r o c k R a n g e . S i m i l a r l y the 171 f a u l t s a l o n g t h e s o u t h f l a n k of t h e S h e e p r o c k M o u n t a i n s w e r e r e j u v e n a t e d . The n e t w o r k of f a u l t s n o r t h of B l a c k ' s R a n c h and on the s o u t h w e s t end of t h e S h e e p r o c k M o u n t a i n s a f f e c t i n g O r d o v i c i an r o c k s i s p r o b a b l y of M i o c e n e age and m a y r e p r e s e n t c o l l a p se s t r u c t u r e s which a t t e n d t h e e x t r u s i o n of r h y o l i t e s and a n d e s i t es i n t h o s e a r e a s. P l i o c e n e f a u l t m o v e m e n t s - F a u l t i n g r e s u m e d in Late(?) P l i o c e n e and p e d i m e n t s u r f a c e s f o r m e d d u r i n g l a t e ( ? ) M i o c e ne and e a r l y P l i o c e n e t i m e w e r e r e - e l e v a t e d and a n e w p e r i o d of e r o s i o n i n i t i a t e d . The d i s p l a c e m e n t s w e r e m a i n l y c o n f i n e d to t h e o l d e r n o r t h - s o u t h f a u l t s . The f a u l t s f l a n k i n g t h e r a n g e on the n o r t h and e a s t p r o b a b l y c a m e i n t o e x i s t e n c e at t h i s t i m e . The e a s t - w e s t , s o u t h - f a c i n g , e r o s i o n a l s c a r p at E r i c k s o n P a ss i n d i c a t e s t h a t t h e s o u t h f l a n k f a u l t s w e r e a g a i n a c t i v e and the e a r l y ( ? ) P l i o c e n e s u r f a c e n o r t h of t h e p a s s was e l e v a t e d s e v e r al h u n d r e d f e e t. P l e i s t o c e n e and R e c e n t f a u l t m o v e m e n t s - The m o s t r e c e nt r e c o g n i z a b l e f a u l t s c a r p s a r e t h o s e of t h e n o r t h and e a s t f l a n k i ng f a u l t s . D i s p l a c e m e n t s of r e c e n t a l l u v i um m a y be t r a c e d f r o m the m o u t h of B e n n i o n C a n y o n n o r t h w e s t w a r d to E a s t G o v e r n m e n t C r e e k, t h e n c e n o r t h to t h e L o o k o u t P a s s r o a d . The p r e s e n c e of s l u m p and g r a b e n s t r u c t u r e s in u n c o n s o l i d a t e d fan and t e r r a c e g r a v e l s s u g g e s ts 172 t h a t t h e l a t e s t m o v e m e n t a l o n g t h e s e f a u l t s o c c u r r e d within the l a s t f ew h u n d r e d y e a r s . O r o g e n i c p h a s es G e n e r a l s t a t e m e n t - The o n l y a b s o l u t e d a t e s i n t h e o r o g e n ic h i s t o r y of t h e S h e e p r o c k a r e a a r e t h o s e a f f o r d e d by t h e P e n n s y i v a n i an s t r a t a , the M i o c e n e age of t h e S h e e p r o c k g r a n i t e , and t h e p r e s e n t. An i n t r u s i v e in the n e a r b y E a s t T i n t i c Range i s p r o b a b l y E o c e n e , ana! a m o n z o n i t e in t h e West T i n t i c R a n g e s e e m t o b e r e l a t e d . The s u c c e s s i o n of o r o g e n i c e v e n t s which i s e s t a b l i s h e d by s t r u c t u r al a n d i n t r u s i v e r e l a t i o n s , i s t h e n f i t t e d to t h e s e f ew g u i d e p o s t s as well a s p o s s i b l e , and at t h e s a m e t i m e the c h r o n o l o g i e s of n e a r by a r e a s a r e r e s p e c t e d . The f i r s t t h r e e m a j o r d e f o r m a t i o n a i p h a s es of t h e S h e e p r o c k a r e a t h e r e b y s e e m b e s t a s s i g n e d to t h e C e d ar H i l l s , e a r l y L a r a m i d e and m i d - L a r a m i d e o r o g e n i e s ( s e e E a r d l e y 's u s a g e , 1951). C e d a r H i l l s o r o g e n y ( ? ) - M i d - C r e t a c e o u s p h a s e - The m o n o c l i ne t h a t d o m i n a t e s the S h e e p r o c k M o u n t a i n s was found in e a r l y d e f o r m a t i o n ai t i m e s and p r e - d a t e s the t h r u s t i n g which s e e m s to b e e a r l y L a r a m i d e in a g e . This d e f o r m a t i o n a i p h a s e m a y t h e n b e t h e C e d a r H i l l s o r o g e ny ( E a r d l e y , 1 9 5 1 , p . 273). E a r l y L a r a m i d e o r o g e n y - M o n t a n a p h a s e - The e a r l i e s t p h a se of L a r a m i d e o r o g e n y b e g a n by s i m p l e f o l d i n g which d e v e l o p e d i n to e x t e n s i v e t h r u s t i n g at i t s c u l m i n a t i o n . Great m a s s e s w e r e t h r u st 173 e a s t w a r d and i n p l a e e s o v e r r o d e t h e u p t u r n e d r o c k s of t h e p r e v i o us e p i s o d e of t i l t i n g . The D e a t h C a n y o n and P o l e C a n y o n a n t i c l i n es w e r e f o r m e d d u r i n g t h e M o n t a n a p h a s e . The P o l e Canyon a n t i c l i ne was o v e r t u r n e d and t h r u s t in i m b r i c a t e s h e e t s e a s t w a r d o v e r t i l t ed P r e c a m b r i a n r o c k s . The o l d e s t s t r u c t u r e r e s u l t i n g f r o m t h is p h a s e i s t h e S h e e p r o c k t h r u s t , which i s r e c o g n i z e d by m e a n s of windows In t h e P r e c a m b r i a n r o c k s of t h e u p p e r p l a t e . In t h e West T i n t i c a r e a c a r b o n a t e s t r a t a of t h e l o w e r p l a t e r a n g i n g in a g e f r om C a m b r i a n t h r o u g h D e v o n i a n a r e v e r t i c a l to o v e r t u r n e d and a re b e l i e v e d to i n d i c a t e t h r u s t i n g f r o m the w e s t . In t h e A l l i s o n K n o l l s, O r d o v i c i a n r o c k s a s s i g n e d to t h e F i s h H a v e n d o l o m i t e h a v e b e en t h r u s t o v e r P r e c a m b r i a n t i l l i t e s . The t i l l i t e s i n t h i s a r e a dip i d e n t i c a l l y with t h e r e s t of t h e P r e c a m b r i a n r o c k s of t h e n o r t h w e s t - t r e n d i n g l i n e of s m a l l k n o l l s which e x t e n d t o w a r d E r i c k s o n s K n o l l. T h i s d i p i s s i m i l a r to t h o s e of t h e s m a l l P r e c a m b r i a n o u t c r o p s west of South P i n e Canyon and t h e r e s t of t h e r o c k s of t h e S h e e p r o c k m o n o c l i n e . In t h e S i m p s o n M o u n t a i n s the t h r u s t i n g of C a m b r i a n and P r e c a m b r i a n s t r a t a o v e r O r d o v i c i a n r o c k s i s a s s i g n e d to t h e m a i n p e r i od of t h r u s t i n g of t h i s p h a s e . The a i l o c h t h o n o u s b l o c k s of t h e O q u i r rh ( P e n n s y l v a n i a ^ f o r m a t i o n , which a r e in t h r u s t c o n t a c t with O r d o v i c i an t h r o u g h M i s s i s s i p p i a n r o c k s In t h e n o r t h end of t h e W e s t Lookout H i l l s , a r e a s s i g n e d to t h e S h e e p r o c k t h r u s t i n g p h a s e of t h e o r o g e n y. The s i m i l a r i t y in d i p of b o t h t h e u p p e r and l o w e r p l a t e s p r o v e s the 174 t h r u s t i n g i s p o s t - t i l t i n g . This t h r u s t i s b e l i e v e d t o b e r e l a t e d to t h e t h r u s t i n g in t h e ( L o s R i c o s t h r u s t ) n o r t h e r n O n a q u i M o u n t a i ns w h i c h i s c o n s i d e r e d by C r o f t ( 1 9 5 6 , p„ 30) t o b e of t h e e a r l y L a r a - m i d e o r o g e n y „ During t h i s p h a s e , the m o n o c l i n a l s t r u c t u r e a c t i ng s o m e w h a t a s a b u t t r e s s was d i s p l a c e d to t h e e a s t . The n o r t h e r n p a rt of t h e m o n o c l i n e m o v e d f a r t h e r e a s t t h a n the s o u t h e r n s e g m e n t. T h e i n i t i a l m o v e m e n t s on t h e n o r t h - d i p p i n g , s t r i k e - s l i p f a u l t s at G o v e r n m e n t C r e e k , Red P i n e C r e e k , and L o o k o u t P a s s p r o b a b ly o c c u r r e d at t h i s t i m e . The n o r t h d i p of t h e f a u l t s i s b e l i e v e d to be t h e r e s u l t of a w r a p p i n g of f o r c e s a r o u n d the m a i n m a s s of t h e m o n o c l i n e . The r e s i s t a n c e of t h e m o n o c l i n a l b l o c k i m p a r t e d a r e l a t i v e ly s t r o n g s o u t h w e s t e r l y v e c t o r to t h e m a i n e a s t e r l y d i r e c t e d f o r c e . The O n a q u i f a u l t , a t r a n s v e r s e f a u l t s e p a r a t i n g t h e S h e e p r o c k a r e a f r om t h e O n a q u i - S t a n s b u r y R a n g e s , f o r m e d at t h i s t i m e . The Onaqui f a u l t i s p r i n c i p a l l y a s t r i k e - s l i p f a u l t n o r t h of which t h e s t r a t a y i e l d ed t o f o r m f o l d s and t h r u s t s ; to t h e s o u t h t h e p r e s e n c e of t h e t i l t ed s t r a t a o f f e r e d m o r e r e s i s t a n c e which r e s u l t e d In s t r i k e - s l i p m o v e m e n t s and t h r u s t i n g of m o r e c o m p e t e n t m a s s e s . M I d - L a r a m i d e o r o g e n y ( ? ) - P a l e o c e n e p h a s e - F o l l o w i n g the w e s t - t o = e a s t c o m p r e s s i v e p h a s e of M o n t a n a ( ? ) t i m e , p o s s i b l y a f t er a p e r i o d of r e l a t i v e q u i e s c e n c e , o r o g e n i c a c t i v i t y o n c e a g a i n a f f e c t ed t h e S h e e p r o c k a r e a . F o r c e s d i r e c t e d In a s o u t h e r l y and s o u t h w e s t e r ly d i r e c t i o n c a u s e d l a r g e m a s s e s of t h e m o n o c l i n e to b e t h r u s t a f ew 175 m i l e s to t h e s o u t h w e s t , o v e r r i d i n g and t r u n c a t i n g p r e - e x i s t i ng f o l d s and t h r u s t s . The n o r t h - d i p p i n g P o l e C a n y o n t h r u s t o v e r r o de t h e o v e r t u r n e d l i m b of t h e P o l e Canyon a n t i c l i n e . The L i o n Hill t h r u s t and r e l a t e d n o r t h f l a n k t h r u s t s of s m a l l e r s o u t h e r l y d i s p l a c e m e n t s a r e a l s o a s s i g n e d to t h i s p h a s e . M o v e m e n t s along s t r i k e - s l i p f a u l t s of an e a r l i e r o r o g e n i c p h a s e w e r e p r o b a b l y r e n e w ed at t h i s t i m e. L a t e L a r a m i d e _orogenjy - F o l l o w i n g the p e r i o d of c o m p r e s s i on t h e W e s t T i n t i c m o n z o n i t e was i n t r u d e d i n t o t h e s t r a t a n e a r the e a s t e r n end of the S h e e p r o c k M o u n t a i n s , The i n t r u s i v e c u t s both t h e u p p e r and l o w e r p l a t e s of t h e S h e e p r o c k t h r u s t and t h e s t r a t a of t h e o v e r t u r n e d l i m b of t h e P o l e Canyon a n t i c l i n e . The West T i n t ic m o n z o n i t e i s o l d e r t h a n t h e S h e e p r o c k g r a n i t e which i s M i o c e n e in a g e . An E o c e n e o r O l i g o c e n e age f o r the m o n z o n i t e i s p o s t u l a t ed b e c a u s e of i t s age r e l a t i v e to t h e g r a n i t e and I t s s i m i l a r i t y with the E a s t T i n t i c i n t r u s i v e which i s p r o b a b l y E o c e n e in a g e ( M o r r i s , 1955, p e r s o n a l c o m m u n i c a t i o n ) . The West T i n t i c i n t r u s i v e p r o b a b l y m a r k ed t h e end of L a r a m i d e a c t i v i t y in t h e S h e e p r o c k a r e a. B a s i n and R a n ^ e p h a s e - F o l l o w i n g an e x t e n s i v e p e r i o d of e r o s i on d u r i n g O l i g o c e n e and e a r l y M i o c e n e , the S h e e p r o c k a r e a was a g a i n u p l i f t e d , T e n s i o n a l f a u l t s a l o n g t h e s o u t h and w e s t s i d e s of t he S h e e p r o c k r a n g e w e r e i n i t i a t e d o r r e a c t i v a t e d . The S h e e p r o c k g r a n i te w a s i n t r u d e d at t h i s t i m e a n d m a n y of t h e s m a l l n o r m a l f a u l t s s u r r o u n d i ng 176 t h e i n t r u s i v e w e r e f o r m e d . The a r e a l y i n g b e t w e e n the h i g h er p o r t i o n s of the S h e e p r o c k and S i m p s o n M o u n t a i n s was c o m p l e x ly f a u l t e d at t h i s t i m e . Volcanic r o c k s l o c a t e d in t h e s a m e a r e a w e re e r u p t e d . Another p e r i o d of e r o s i o n s e p a r a t e d the M i o c e n e f a u l t i ng f r o m the P l i o c e n e . During l a t e ( ? ) P l i o c e n e , r e n e w e d f a u l t i ng e s t a b l i s h e d n e w b a s e l e v e l s a n d l o w e r p e d i m e n t s w e r e f o r m e d. V e r y young s c a r p s in u n c o n s o l i d a t e d m a t e r i a l a l o n g t h e n o r t h s i de of the S h e e p r o c k R a n g e i n d i c a t e r e n e w e d f a u l t i n g in R e c e n t t i m e. 177 GEOMORPHOLOGY G e n e r a l f e a t u r es T h e n o r t h - t r e n d i n g s e g m e n t of t h e S h e e p r o c k Range j o i n s the L o o k o u t H i l l s on t h e n o r t h at R e d P i n e C a n y o n . The L o o k o u t H i l ls f o r m a l i n k with t h e n o r t h - l y i n g Onaqui M o u n t a i n s . The e a s t - w e st t r e n d i n g s e g m e n t of t h e S h e e p r o c k R a n g e on t h e s o u t h c o m b i n es wit h t h e n o r t h - t r e n d i n g s e g m e n t to p r o d u c e a d r a i n a g e s y s t em d o m i n a n t i y to t h e n o r t h - n o r t h e a s t and to t h e s o u t h . D r a i n a g e to t he n o r t h - n o r t h e a s t i s i n t o R u s h V a l l e y and t o t h e west i n t o Skull V a l l e y. T h e s o u t h f l a n k d r a i n s i n t o t h e s i n k s of t h e ' O l d R i v e r B e d 1 , t h e p r e h i s t o r i c r i v e r c o n n e c t i n g t h e S e v i e r e m b a y m e n t with t h e m a i n body of w a t e r of L a k e B o n n e v i l l e. S e d i m e n t a r y r o c k s of t h e S h e e p r o c k R a n g e d i p d o m i n a n t i y to t h e n o r t h , a n d t h e p r e s e n t t o p o g r a p h y r e f l e c t s s t r o n g l y t h e e r o s i on of t h i s s t r u c t u r e . Dip s l o p e s a r e p r o m i n e n t n o r t h e a s t of t h e d i v i de w h e r e d i f f e r e n t i a l w e a t h e r i n g h a s i n f l u e n c e d the t e r r a n e . The s o u t h and w e s t s l o p e s a r e l e s s s t e e p t h a n t h e n o r t h e a s t s l o p e s, and t h e d r a i n a g e i s m o r e s i n u o u s . The g r a n i t e c r a g s , s t e ep s l o p e s , and V - s h a p e d v a l l e y s i n d i c a t e t h e a r e a i s i n t h e 'youthful* e r o s i o n s t a g e . Five p r i n c i p a l i a n d f o r m s a r e r e c o g n i z e d : (1) f a u lt s c a r p s , (2) p e d i m e n t s , (3) a l l u v i a l f a n s , (4), l a c u s t r i n e f e a t u r e s, a n d (5) g l a c i a l I a n d f o r m s. 178 F a u l t s c a r ps G e n e r a l •* F a u l t s c a r p s o u t l i n e t h e m a i n m a s s of t h e S h e e p r o ck R a n g e . The o l d e s t f a u l t s a r e the west and s o u t h f l a n k i n g f a u l t s, w h e r e a s t h e n o r t h and e a s t f l a n k i n g f a u l t s a r e m o r e r e c e n t ( s ee G e o l o g i c m a p , P l a t e I ). W e s t F l a n k f a u l t <= T h e w e s t e r n e s c a r p m e n t 8 f o r m e d by t he W e s t F l a n k f a u l t , r i s e s a b r u p t l y 1, 500 to 2, 000 f e e t f r o m the ' h i gh l e v e l ' p e d i m e n t at t h e h e a d of W e s t Oak B r u s h C r e e k . As a s s o c i a t ed f a u l t one m i l e w e s t of t h e m a i n f r a c t u r e c u t s t h e h i g h l e v e l p e d i m e nt and f u r t h e r a c c e n t u a t e s the t o p o g r a p h y . The W e s t F l a n k f a u l t i s o f f s et t o t h e w e s t by a r e v e r s e s t r i k e - s l i p f a u l t n e a r t h e h e a d of West G o v e r n m e n t C r e e k . S p r i n g s and s e e p s m a r k t h e f a u l t l i n e a s do s m a ll d e p r e s s e d s a d d l e s at t h e j u n c t i o n of t h e p e d i m e n t s u r f a c e with the m o u n t a i n f r o n t . The d i s s e c t i o n of t h e o l d e r and y o u n g e r p e d i m e n t s of G o v e r n m e n t V a l l e y i n d i c a t e s r e c u r r e n t uplift and m o v e m e n t a l o n g the West F l a n k and a s s o c i a t e d f a u l t s which f o r m the g r a b e n = l i k e s t r u c t u re b e t w e e n t h e S h e e p r o c k and t h e S i m p s o n M o u n t a i n s. S o u t h F l a n k f a u l t - The South F l a n k f a u l t i s p o o r l y m a r k e d , b e l ng n e a r the j u n c t i o n of t h e g r a n i t e with t h e f l a n k i n g p e d i m e n t . Loughlin ( 1 9 2 0 , p . 424) n o t e d t h e g r a d i e n t c h a n g e of t h e s t r e a m s n e a r the m o u t h of t h e c a n y o n s a l o n g t h e s o u t h s i d e of t h e r a n g e . The c h a n ge of g r a d e o r ' n i c k p o i n t ' d o e s n o t r e p r e s e n t t h e m a i n South F l a n k f a u l t. T h e ' n i c k p o i n t ' - i s in i t s p r e s e n t p o s i t i o n b e c a u s e of e r o s i o n and 179 p e d i m e n t a t i o n . The m a i n v e r t i c a l m o v e m e n t i s a l o n g a z o n e of a p p r o x i m a t e l y p a r a l l e l f a u l t s ; the z o n e e x t e n d s f r o m the g r a n i t e about -one m i l e i n t o t h e v a l l e y . The e x a c t t r a c e s of t h e f a u l t s c a n o n l y be e s t i m a t e d s i n c e p e d i m e n t g r a v e l s m a s k m o s t of t h e b e d r o c k. N o r t h a n d e a s t f l a n k i n g f a u l t s - Recent m o v e m e n t a l o n g t h e n o r th and e a s t f l a n k i n g f a u l t s i s i n d i c a t e d by low s c a r p s c u t t i n g f a n g r a v e ls c l o s e to t h e m o u n t a i n f r o n t . These low s c a r p s h a v e not b e e n d i s s e c t ed and a r e p r o b a b l y of v e r y r e c e n t a g e . G r a b e n s and l a n d s l i d e s a s s o c i a t ed wit h t h e f a u l t i n g a r e p r e s e n t n e a r t h e mcouths of N o r t h Oak B r u s h and H a r k e r C a n y o n s. P e d i m e n t s G e n e r a l - P e d i m e n t s of s e v e r a l p e r i o d s of u p l i f t a r e e v i d e n t along t h e west and s o u t h s i d e s of t h e S h e e p r o c k R a n g e . The p e d i m e n t s a re c l a s s i f i e d a s h i g h - l e v e l and l o w - l e v e l ( P l a t e XXV). H i g h - l e v e l p e d i m e n t s - The o l d e s t p e d i m e n t s u r f a c e i s n o t ed n e a r t h e h e a d s of E l d e r b e r r y , Dry and W e s t Oak B r u s h C a n y o n s. The s p u r s a r e r o u n d e d and a p p e a r a s m a t u r e s u r f a c e s. T h e h i g h e s t p a r t s of t h e S h e e p r o c k s t o c k a l s o a p p e a r t o b e t r u n c a t e d by an a n c i e n t e r o s i o n s u r f a c e and c o n t a i n c o n c a v e s l o p e s and p e r c h e d s h a l l o w m a t u r e v a l l e y s which h a v e b e e n d i s s e c t e d by l a t e r e r o s i o n . The E l d e r b e r r y s u r f a c e and t h e s u r f a c e on t h e h i gh p o i n t s of t h e g r a n i t e m a y be p a r t s of a s i n g l e e r o s i o n s u r f a c e. High, t r u n c a t e d , c o l l u v i a l c o v e r e d s p u r s a r e on t h e n o r t h s i de PLATE XX Figure 2 Looking west at Erickson Pass and Pliocene surface; Simpson Mountains in background. Erosional scarp in center of photograph. 180 of E a s t G o v e r n m e n t Canyon and on t h e e a s t s i d e of L o o k o u t V a l l e y. g r a n i t e and v o l c a n i c r o c k s , a r e e v i d e n t on t h e f l a n k s of t h e r a n g e. T h e y a r e v e n e e r e d with a l l u v i um which r a n g e s f r o m a f ew f e et t o o v e r 100 f e e t t h i c k . S e v e r a l e p i s o d e s of u p l i f t a r e n o t e d by the p e r c h e d t e r r a c e - l i k e s u r f a c e s above t h e p r e s e n t day g r a d i e n t . The p e d i m e n t g r a v e l shown on t h e m a p i n c l u d e s d e b r i s - b u i l t s u r f a c e which e x t e n d s t h e p e d i m e n t s u r f a c e i n t o t h e v a l l e y . All t h e p e d i m e n t s u r f a c es a r e d i s s e c t e d by d e e p g u l l i e s , e s p e c i a l l y n e a r t h e i r u p p e r e x t r e m i t i e s. A l l u v i a l f a n s of m o r e r e c e n t age t h a n t h e p e d i m e n t s u r f a c es s u r r o u n d the r a n g e. T h e s o u t h s i d e of t h e S i m p s o n M o u n t a i n s i s f l a n k e d by a l l u v i al f a n s , m a n y of which c o a l e s c e in t h e i r l o w e r r e a c h e s f o r m i n g a b a j a d a which e x t e n d s i n t o t h e Old R i v e r B e d . A s t u d y of a e r i al p h o t o g r a p h s of t h e S i m p s o n M o u n t a i n s r e v e a l s t h a t m u c h of the d i s s e c t i o n of t h e p e d i m e n t s and a l l u v i a l f a n s c o i n c i d e s with t he t e n u r e of L a k e B o n n e v i l l e . The f a n s which w e r e p a r t i a l l y c o v e r ed by B o n n e v i l l e w a t e r s a r e m o r e d i s s e c t e d above t h e o l d w a t e r l e v e l. The l i m i t e d and s p o r a d i c n a t u r e of the p r e c i p i t a t i o n of t h e p r e s e nt day c l i m a t e i s c a u s i n g a l l u v i a t i o n n e a r the a p i c e s of t h e f a n s. F a n s on t h e n o r t h s i d e of t h e S h e e p r o c k Range and on t h e e a st s i d e of t h e E a s t L o o k o u t H i l l s g r a d e i n t o s o i l - c o v e r e d a l l u v i um G e n t l y s l o p i n g s u r f a c e s , e r o d e d in A l l u v i a l f a ns 181 w h e r e t h e f a r m l a n d s a r o u n d V e r n o n , Utah, at t h e s o u t h e r n e n d of R u s h V a l l e y a r e l o c a t e d. L a c u s t r i n e I a n d f o r ms T o p o g r a p h i c f e a t u r e s a s s o c i a t e d with L a k e B o n n e v i l l e i n c l u d e wave c u t b e a c h e s , w a v e - b u i l t t e r r a c e s , and o f f s h o r e b a r s . L a c u s t r i ne d e p o s i t s a r e p r e s e n t in Skull V a l l e y and In t h e n o r t h e r n p a r t of t he S e v i e r D e s e r t ( G i l b e r t , 1890). T h e m o s t p r o m i n e n t w a v e - c u t b e a c h and w a v e - b u i l t t e r r a c e i s t h at of t h e B o n n e v i l l e s h o r e l i n e at an e l e v a t i o n of 5 , 1 3 5 f e e t . Other s h o r e l i n e s of l o w e r l a k e s t a g e s a r e i n d i s t i n c t. I n a r e a s of g e n t l e s l o p e s , f a i n t r e m n a n t s of s m a l l o f f s h o r e b a rs and b e r m s ( s t o r m b e a c h e d ) o c c u r . T h e s e a r e e s p e c i a l l y n o t i c e a b le w h e r e t h e M e a d o w C r e e k d r a i n a g e i n t e r s e c t s the s h o r e l i n e. P o o r l y d e v e l o p e d , r o c k y w a v e - c u t b e a c h e s a r e p r e s e n t along t h e w e s t s i d e of A l l i s o n K n o l l s. A s s o c i a t e d l a c u s t r i n e d e p o s i t s a r e of s a n d , s i l t , and c l a y. G l a c i a l I a n d f o r ms P o s s i b l e e v i d e n c e of g l a c i a t i o n in t h e S h e e p r o c k M o u n t a i n s was n o t e d at o n l y one l o c a l i t y - N o r t h Oak B r u s h C a n y o n . North Oak B r u s h C a n y o n i s U - s h a p e d In c r o s s - s e c t i o n and at i t s m o u t h i s a d e p o s i t of l a r g e b o u l d e r s w h i c h m a y r e p r e s e n t a t e r m i n a l m o r a i n e. T h e h e a d of t h e c a n y o n i s v e r y s t e e p and p r o b a b l y r e p r e s e n t s a p o o r l y d e v e l o p e d c i r q u e b a s i n . P r e c i p i t o u s n o r t h - f a c i n g s l o p es 182 p r e s e n t a l o n g t h e d i v i d e f r o m T a l a w a g C a n y o n to D u t c h P e a k m ay r e p r e s e n t e r o s i o n a l f e a t u r e s of n i v a t i o n c e n t e r s which w e r e p r e s e nt a l o n g t h e n o r t h f l a n k of t h e d i v i d e d u r i n g P l e i s t o c e n e t i m e. 183 ECONOMIC GEOLOGY O r e d e p o s i ts T h e o r e d e p o s i t s of the B l u e B e l l , C o l u m b i a , E r i c k s o n , and West T i n t i c m i n i n g d i s t r i c t s ( F i g u r e 6) a r e a s s o c i a t e d with the two m a i n i n t r u s i v e m a s s e s , the W e s t T i n t i c m o n z o n i t e and the S h e e p r o c k g r a n i t e , and s i n c e t h e two s t o c k s a r e of d i f f e r e n t a g e s, two p h a s e s of m i n e r a l i z a t i o n a r e s u g g e s t e d . This s e e m s p r o b a b ly a l s o b e c a u s e t h e g r o u p s of m i n e r a l s p r e s e n t in a s s o c i a t i o n with e a c h a r e d i f f e r e n t . It h a s b e e n c o n c l u d e d t h a t t h e m o n z o n i t e is p r o b a b l y e a r l y T e r t i a r y and t h e g r a n i t e i s m i d d l e to l a t e M i o c e n e, and h e n c e t h e s e a g e s a r e p r e s u m e d to b e t h o s e of t h e two p h a s e s of m i n e r a l i z a t i o n . T h e e a r l y T e r t i a r y ( ? ) d e p o s i t s h a v e y i e l d e d m o s t of t h e p r o d u c t i on i n t h e W e s t T i n t i c d i s t r i c t . S i l v e r , lead, gold, z i n c , and t u n g s t en c o m p r i s e the m e t a l s t h a t h a v e b e e n c o m m e r c i a l in t h e d i s t r i c t. L e a d - s i l v e r - g o l d - z i n c f i s s u r e - f i l l i n g , r e p l a c e m e n t b o d i e s and t u n g s t e n - b e a r i n g , c o n t a c t m e t a m o r p h i c z o n e s a r e the c h i e f t y p es of c o m m e r c i a l d e p o s i t s in t h e a r e a. M i o c e n e and l a t e r d e p o s i t s i n c l u d e the f i s s u r e - f i l l i n g v e i ns a s s o c i a t e d with f a u l t i n g due to i n t r u s i o n of t h e S h e e p r o c k g r a n i t e. C o p p e r - f l u o r i t e , l e a d - z i $ c , m a n g a n e s e - f luo r i t e - u r a n i u m v e i ns r e p r e s e n t m o s t of t h e o r e and p-rofore d e p o s i t s a s s o c i a t e d with INDEX M A P SHOWING LOCATION OF M I N I N G D I S T R I C T S IN T H E S H E E P R O C K MOUNTAIN; O I 2 3 4 5 *9 SCALE MILES F I G U R E 6 184 t h e g r a n i t e . Contact d e p o s i t s and f i s s u r e d e p o s i t s within t h e g r a n i te c o n t a i n s o m e v a l u e s of t u n g s t e n , Syngenetic d e p o s i t s i n c l u de d i s s e m i n a t e d s e g r e g a t i o n s of b e r y l n e a r t h e c e n t e r of t h e S h e e p r o ck s t o c k . Most of t h e o l d m i n e w o r k i n g s in t h e S h e e p r o c k a r e a a r e i n a c c e s s i b l e and c o n s e q u e n t l y l i t t l e c a n b e a d d e d to e a r l i e r r e s u m es of t h e d e p o s i t s ( B u t l e r , et a l , 1920), H o w e v e r , an a t t e m p t was m a de t o r e l a t e t h e d e p o s i t s to v a r i o u s p h a s e s of i g n e o u s a c t i v i t y and to r e p o r t on m o r e r e c e n t d e v e l o p m e n t s within t h e a r e a. T h e d e p o s i t s of t h e W e s t T i n t i c d i s t r i c t will not b e d i s c u s s ed i n t h i s p a p e r , and f o r i n f o r m a t i o n c o n c e r n i n g t h e m , s e e U. S, G e o l o g i c a l S u r v e y , P r o f e s s i o n a l P a p e r 1 1 1 , O r e D e p o s i t s of U t a h. H i s t o r y and p r o d u c t i on S h o r t l y a f t e r o r e was d i s c o v e r e d in t h e E a s t T i n t i c a r e a in 1869, p r o s p e c t o r s c l a i m e d g r o u n d in t h e W e s t T i n t i c a r e a , and t h e d i s t r i ct was o r g a n i z e d in 1 8 7 0 . In 1871 t h e C o l u m b i a m i n i n g d i s t r i c t was o r g a n i z e d and was f o l l o w e d in 1894 by t h e o r g a n i z a t i o n of t h e E r i c k s on o r B l a c k C r o o k d i s t r i c t , and l a t e r in 1896 t h e B l u e B e l l d i s t r i c t was o r g a n i z e d . P r o d u c t i o n f r o m the f o u r d i s t r i c t s within t h e S h e e p r o c k a r ea h a s b e e n m e a g e r . The W e s t T i n t i c d i s t r i c t p r o d u c e d a c o n s i d e r a b le q u a n t i t y of l e a d , z i n c , s i l v e r , and g o l d in e a r l i e r y e a r s and d u r i ng W o r l d War II s o m e t u n g s t e n was s h i p p e d f r o m t h e m i n e s n e a r the 185 e a s t e r n p e r i p h e r y of t h e m o n z o n i t e . The B l a c k Hawk m i n e h as b e e n t h e p r i n c i p a l p r o d u c e r of t h e B l u e B e l l d i s t r i c t . Lead o re v a l u e d at 40 to 50 t h o u s a n d d o l l a r s h a s b e e n p r o d u c e d f r o m the B l a c k Hawk p r o p e r t y . The C o l u m b i a and E a s t E r i c k s o n d i s t r i c ts h a v e p r o d u c e d only t o k e n a m o u n t s of o r e , p r i n c i p a l l y l e a d - z i n c. C o l u m b i a d i s t r i ct L o c a t i o n - The C o l u m b i a d i s t r i c t l i e s on t h e e a s t s i d e of the S h e e p r o c k M o u n t a i n s in T o o e l e County, n o r t h of t h e B l u e B e ll d i s t r i c t . The d e p o s i t s of t h e d i s t r i c t a r e r e l a t e d to t h e S h e e p r o ck s t o c k of M i o c e n e a g e. L e a d - z i n c v e i n s - The S h a r p m i n e i s n e a r t h e h e a d of H a r k er C a n y o n on t h e n o r t h s i d e of t h e S h e e p r o c k R a n g e . The m i n e p o r t a l is i n C a m b r i a n s l a t e s and q u a r t z i t e s , which d i p s t e e p l y n o r t h w a r d. V. C. H e i k e s r e p o r t s (1920, p . 426): " S i n c e 1880 t h e S h a r p m i n e , a l e a d - s i l v e r - z i nc p r o p e r t y h a s b e e n t h e o n l y n o t a b l e p r o d u c e r . In t h e l a t e r p a r t of 1 9 0 8 , a 5 0 - t o n c o n c e n t r a t o r, e q u i p p e d with r o l l s , H u n t i n g t o n s c r e e n j i b s , and W i l f i e y t a b l e s , was b u i l t . Some l e a d c o n c e n t r a te w a s s h i p p e d in 1908 and 1909, and s h i p m e n t s of l e a d - z i n c s u l p h i d e s h a v e b e e n r e p o r t e d . In 1914 t h e l e s s e e s w e r e s h i p p i n g a f a i r g r a d e of c r u de o r e . F u r t h e r , L o u g h l i n r e p o r t s (1920, p . 429): " A c c o r d i n g to L . D. G o r d o n , a f o r m e r o p e r a t or of t h e m i n e , the l e a d c a r b o n a t e o r e c o n t a i n ed about 40 p e r c e n t l e a d and 20 o u n c e s of s i l v e r to t h e ton, and t h e m i x e d s u l p h i d e o r e about 30 p e r c e n t l e a d and 25 p e r c e n t z i n c . The m i ne 186 " h a s b e e n workecd t h r o u g h t u n n e l s a g g r e g a t i n g 1, 250 f e e t i n length,, The m a i n t u n n e l when v i s i t e d was c a v e d i n , and a s m a l l s t r e a m of w a t e r i s s u e d f r om i t . The o r e on t h e d u m p I n c l u d e d b o t h p r i m a ry s u l p h i d e , l e a d c a r b o n a t e , and l i m o n i t e but n o t h i ng i s known of t h e i r r e l a t i v e a m o u n t s . The wail r o ck I n c l u d e s a l a r g e a m o u n t of t h e c h l o r i t i c b e d s t h at h a v e b e e n r e p l a c e d and i m p r e g n a t e d to s o m e e x t e nt by o r e . T h e S h a r p m i n e and the B e n m o r e m i n e w e r e v i s i t e d b y t he w r i t e r In 1 9 5 5 - 5 6 . Both w e r e i n a c c e s s i b l e ; t h e S h a r p m i n e was c a v e d f o r a d i s t a n c e of o v e r 100 f e e t f r o m the p o r t a l , and the B e n m o r e m i n e , a s h o r t d i s t a n c e w e s t of t h e S h a r p p o r t a l , was c a v ed n e a r i t s p o r t a l . Water i s s u e s f r o m both m i n e s and i s s u f f i c i e n t l y, r i c h i n I r o n t o s t a i n r o c k s n e a r t h e p o r t a l s . S p e c i m e n s of r o c k s f r om t h e d u m p of t h e S h a r p m i n e I n d i c a t e ^ as L o u g h l i n o b s e r v e d , that the o r e , which i s p r i n c i p a l l y lead-=zinc, f i l l s f r a c t u r e s and f a u l t z o n e s. D r u s y and c o m b q u a r t z i s m i x e d with g a l e n a and s p h a l e r i t e . A f ew r o c k s c o n t a i n e d only white q u a r t z and p y r l t e . Some s a m p l e s of c h l o r i t i c wall r o c k w e r e r e p l a c e d by g a l e n a and q u a r t z , P y r i t i z a t i on i s p r o m i n e n t i n s o m e of t h e q u a r t z l t e s . B e s i d e s g r e e n , t i l l i t ic s l a t e s , the wall r o c k s p e n e t r a t e d c o n s i s t of g r a y q u a r t z i t e c o n g l o m e r a te and b l a c k m i c a c e o u s s l a t e. T h e t r e n d of t h e m i n e r a l i z e d z o n e s c o u l d n o t b e t r a c e d by s u r f a ce e x p o s u r e s ; h o w e v e r , t h e r e i s a s t r o n g s h e a r zone which e x t e n d s n e a r ly due w e s t , s o u t h e a s t of t h e p r o p e r t y . G o s s a n f r o m the s h e a r zone y i e l d s m a n g a n e s e and l i m o n i t e . F a u l t s e x t e n d i n g n o r t h w a r d f r o m the 187 S h e e p r o c k s t o c k h a v e b e e n t r a c e d to t h e n o r t h s i d e of t h e r a n ge a n d m a y at t h e j u n c t u r e of the east-=west s h e a r i n g h a v e b e en f a v o r a b l e f o r c o n c e n t r a t i o n of t h e l e a d ~ z i n c d e p o s i t s i n t h e a r e a of t h e S h a r p m i n e . M a n g a n e s e o x i d e o r e s 9 t o t a l l n g 1,496 long t o n s and a v e r a g i ng 25 p e r c e n t , h a v e b e e n s h i p p e d f r o m the v i c i n i t y of t h e S h a r p m i ne i n t h e 1 9 3 0 ' s by C . W, J e n k i n s ( C r i t t e n d e n , 1951, p . 38)„ T h e S u l t a n a p r o p e r t y i s n o r t h of t h e d i v i d e at t h e h e a d of N o r th Oak B r u s h C a n y o n . The m i n e was not e n t e r e d , but f r o m m a t e r i al on t h e d u m p , s l a t e , q u a r t z i t e , and t i l l i t e w e r e p e n e t r a t e d. L o u g h l i n (1920, p . 429) s t a t e s: " T h e New S u l t a n a o r e body h a d not b e e n o p e n ed a t t h e t i m e of t h e w r i t e r ' s v i s i t i n 1 9 1 2 . It is r e p o r t e d to be a v e i n 4 f e e t t h i c k in q u a r t z i t e, a n d t h e o r e i s s a i d to c o n t a i n 60 c e n t s i n g o ld and 5 o u n c e s i n s i l v e r to t h e t o n , 48 p e r c e nt l e a d , and 28 p e r c e n t i r o n . The z i n c c o n t e nt i s not k n o w n . One h u n d r e d t o n s of o r e a r e s a id t o h a v e b e e n m i n e d in 1 9 1 4 . r T h e r e a r e t h r e e a d i t s on t h e p r o p e r t y and t h e r e m a i n s of a m i ll w h i c h a p p a r e n t l y was n e v e r u t i l i z e d . The w e s t e r n m o s t a d i t s b e ar a p p r o x i m a t e l y N. 90® W. i n t o b l a c k v a r v e d s l a t e c o n t a i n i n g p y r i te and with l i m o n i t e g o s s a n . No o r e was p r o d u c e d f r o m t h i s v e n t u r e, a n d t h e b l a c k s l a t e was t h e o n l y r o c k p e n e t r a t e d . Q u a r t z - f i l l ed b r e c c i a z o n e was i n t e r s e c t e d a s shown by m a t e r i a l on t h e d u m p. An u p p e r a d i t c o m m e n c e s in g r a y q u a r t z i t e and s p o n g y l i m o n i te 188 g o s s a n . L e s s t h a n 100 f e e t of t u n n e l w a s d r i v e n at t h i s p l a c e* T h e m a i n S u l t a n a w o r k i n g s a g g r e g a t e a p p r o x i m a t e ly 300 f e e t of t u n n e l . The p o r t a l I s in s t e e p l y d i p p i n g t a n q u a r t z i te of P r e c a m b r i a n age i m m e d i a t e l y o v e r l y i n g p u r p l e , q u a r t z i t ic t i l l l t e . O r e f r o m the d u m p i s r i c h i n p y r i t e and g a l e n a . Q u a r tz f o r m s the b u l k of t h e g a n g u e m i n e r a l s . One s p e c i m e n c o n s i s t ed of f i n e - g r a i n e d s p e c u l a r h e m a t i t e with l a t e r i n c l u s i o n s of p y r i t e. The o r e i s v e r y s i m i l a r to t h a t of t h e S h a r p m i n e , which i s l e ss t h a n a m i l e to t h e e a s t , P y r i t i z a t i o n of t h e q u a r t z l t e s n e a r the f i s s u r e s r e p r e s e n t s the e x t e n t of t h e a l t e r a t i o n. The I r o n Hope p r o s p e c t , n e a r t h e h e a d of E a s t G o v e r n m e n t Canyon, c o n s i s t s of a s h o r t a d i t and a s h a f t in t h e T i n t i c q u a r t z i t e along a f a u lt a s s o c i a t e d with t h e G o v e r n m e n t C r e e k f a u l t z o n e . The o r e i s s p e c u l a - r i t e and q u a r t z in a q u a r t z i t e f a u l t b r e c c i a which s t r i k e s N, 90° E, a n d d i p s 70° S, Some p o d s of o r e a r e s e v e r a l f e e t in width; h o w e v e r, t h e s t r u c t u r a l s e t t i n g p r e c l u d e s the p o s s i b i l i t y f o r a l a r g e - s c a le c o m m e r c i a l v e n t u r e. B l u e B e l l d i s t r i ct L o c a t i o n - The B l u e B e l l d i s t r i c t l i e s on t h e e a s t s i d e of the S h e e p r o c k M o u n t a i n s n e a r the s o u t h b o u n d a r y of T o o e l e County, T h e d e p o s i t s of t h e d i s t r i c t a r e g e n e r a l l y c o n s i d e r e d to be r e l a t e d to t h e S h e e p r o c k g r a n i t e. 189 L e a d - z i n c v e i n s - F o u r a r e a s c o n t a i n i n g s i g n i f i c a n t l e a d - z i n c v e i n s i n t h e d i s t r i c t a r e t h e B o g a n and an u n n a m e d m i n e at t h e m o u t h of B e n n i o n Canyon, the M o r g a n m i n e , and t h e B l a ck Hawk m i n e . T h e M o r g a n m i n e I s d i s c u s s e d by L o u g h l i n (1920, p . 431) and s i n c e t h a t t i m e no d e t e c t a b l e d e v e l o p m e n t work h a s b e e n d o n e . The M o r g a n p r o p e r t y I s i n t h e l o w e r q u a r t z i t e s e q u e n c e of t h e S h e e p r o ck s e r i e s . The w o r k i n g s f o l l ow f a u l t z o n e s which t r e n d west and s o u t h w e s t . The o r e i s p r i n c i p a l l y g a l e n a with s o m e m a n g a n e s e and q u a r t z. T h e B l a c k Hawk p r o p e r t y I s i m m e d i a t e l y r e m o v e d f r o m the a r e a of t h e m a p , b e i n g a p p r o x i m a t e l y one and one q u a r t e r of a m i le n o r t h e a s t of t h e M o r g a n m i n e . However, the m i n e I s i n a f a u l t zone i n t h e Dutch P e a k t i l l i t e . P r o d u c t i o n f r o m the B l a c k Hawk r e p r e s e n ts t h e b u l k of t h e o r e s h i p p e d f r o m the d i s t r i c t . The o r e f a v o r s f a u lt z o n e s and i s p r i n c i p a l l y g a l e n a and c e r u s s i t e. T h e Bogan m i n e i s at t h e h e a d of B e n n i o n C a n y o n about a half m i l e e a s t of D u t c h P e a k . The m i n e i s i n g r a y q u a r t z i t e i m m e d i a t e ly u n d e r l y i n g t h e P r e c a m b r i a n d i a b a s e . The o r e i s p r i n c i p a l l y g a l e na and I r o n and m a n g a n e s e o x i d e s In q u a r t z g a n g u e . The m i n e was c a v e d but s h o w s e x t e n s i v e d e v e l o p m e n t w o r k . The o r e o c c u r s in f r a c t u r e d z o n e s a s s o c i a t e d with n o r t h - s o u t h f a u l t s . P r o d u c t i on f r o m the p r o p e r t y i s u n k n o w n . B i s m u t h l n i t e was r e p o r t e d f r om t h e p r o p e r t y . R e p o r t s f r o m R i c h a r d E k k e r i n d i c a t e t h a t t h e a r ea 190 of t h e Bogan m i n e was t o h a v e b e e n t h e o b j e c t i v e of t h e P a rk U t a h v e n t u r e l o c a t e d at t h e h e a d of H a r d - t o - B e a t C a n y o n. T h e u n n a m e d m i n e at t h e m o u t h of B e n n i o n C a n y o n i s P r e c a m b r i a n t i l l i t e . The p o r t a l b e a r s S. 45° W, f o l l o w i n g a m i n e r a l i z e d f r a c t u r e zone and c r o s s e s b a r r e n f r a c t u r e s which s t r i k e N. 70° E . and dip 45® N . The o r e c o n s i s t s of light y e l l o w s p h a l e r i t e , g a l e n a , p y r i t e , and q u a r t z . The p y r i t e is p r i n c i p a l l y d i s s e m i n a t e d i n t h e e n c l o s i n g wall r o c k . L a r g e b o u l d e rs of q u a r t z m o n z o n i t e w e r e o b s e r v e d in t h e t i i l i t e , s o m e m e a s u r i ng o v e r two f e e t in d i a m e t e r. L o c a t i o n - The E r i c k s o n ( B l a c k C r o o k ) d i s t r i c t i n c l u d e s the S i m p s o n M o u n t a i n s and t h e w e s t e r n s l o p e s of t h e S h e e p r o c k M o u n t a i ns n o r t h w a r d to G o v e r n m e n t C r e e k . The a r e a d e s c r i b e d in t h i s r e p o rt i n c l u d e s o n l y t h e e a s t e r n p a r t of t h e d i s t r i c t . The d e p o s i t s of the e a s t E r i c k s o n d i s t r i c t a r e c o n s i d e r e d to b e r e l a t e d t o t h e S h e e p r o ck s t o c k and a r e p o s t - m i d - M i o c e n e In a g e. C o p p e r - f l u o r i t e v e i n s - C o p p e r - f l u o r i t e v e i n s l i e n e a r the b a se of g r a n i t e c l i f f s c l o s e l y p a r a l l e l i n g t h e s o u t h f l a n k of t h e r a n g e . The v e i n s f o l l ow N. 45° W. f i s s u r e s which c o i n c i d e with t h e t r e n d of the S o u t h F l a n k f a u l t . Four p r o p e r t i e s c o n s t i t u t e t h e g r o u p which l i es a l o n g t h e t r e n d of t h e v e i n . The S i l v e r S h i e l d ( F l y i n g D u t c h m a n) a n d t h e C o p p e r J a c k m i n e s a r e m o s t e x t e n s i v e l y d e v e l o p e d . The E r i c k s o n d i s t r i ct 191 h i g h w a t e r t a b l e d i s c o u r a g e s shaft s i n k i n g a s p u m p i n g i s n o r m a l ly n e c e s s a r y only a f ew f e e t b e l o w t h e s u r f a c e . The m i n e r a l i z a t i on c a n b e t r a c e d f r o m n e a r t h e m o u t h of B u r n e d Canyon n o r t h w e s t w a rd t o D u t c h m a n H i l l , on the e a s t s i d e of H a r d - t o - B e a t C a n y o n . Sheeting i s e v i d e n t i n t h e v e i n s which o c c u r i n p o r p h y r l t i c g r a n i t e . The v e i ns r a n g e f r o m a f ew i n c h e s to s e v e r a l f e e t in w i d t h . C h a l c o p y r l t e, f l u o r l t e , m a n g a n e s e and p y r i t e c o m p r i s e the p r i n c i p a l v e i n m i n e r a ls In q u a r t z g a n g u e . Much of t h e f l u o r l t e i s d a r k p u r p l e and s e v e r al s p e c i m e n s of t h e o r e c o n t a i n e d r a d i o a c t i v i t y e s t i m a t e d to i n d i c a te i n e x c e s s of 0 . 1 5 p e r c e n t U s O g . The u r a n i u m m i n e r a l w a s not i d e n t i f i e d but m a y be s i m i l a r to t h a t o c c u r r i n g on t h e S i l v e r King c l a i m s a p p r o x i m a t e l y 4 m i l e s to t h e n o r t h w e s t w h e r e u r a n i n i t e was i d e n t i f i e d ( H i l l i e r , 1956, p . 9). A l t e r a t i o n i s m o d e r a t e in t h e g r a n i t e f l a n k i n g t h e m i n e r a l i z ed f i s s u r e s . Much of t h e b i o t l t e i s a l t e r e d to l i m o n i t e and p y r i t i z a t i on i s e v i d e n t . S e c o n d a r y a l t e r a t i o n w i t h i n t h e v e i n s i s p r o m i n e n t. P y r i t e and c h a l c o p y r l t e a r e p a r t i a l l y a l t e r e d to l i m o n i t e . M a l a c h i t e, c h r y s o c o l l a , and t u r q u o i s e a r e l o c a l l y d e v e l o p e d . Ore on t h e d u m ps i n d i c a t e s t h a t s e c o n d a r y a l t e r a t i o n i s l i m i t e d a s u n a l t e r e d s a m p l es a r e a b u n d a n t . The s h a l l o w n e s s of t h e w a t e r t a b l e f u r t h e r I n d i c a t es t h a t e n r i c h e d z o n e s will be s c a r c e. L e a d - z l n c v e i n s - S e v e r a l l e a d - z i n c d e p o s i t s s i m i l a r to t h o se of t h e S h a r p and S u l t a n a m i n e s o c c u r on t h e E r i c k s o n s i d e of the 192 d i v i d e . They a r e t h e T i n t i c - D e l a w a r e ( f o r m e r F r e e C o i n a g e) i n A l b e r t E k k e r Canyon, the I n d i a n a p o l i s in South P i n e Canyon, a n d t h e D u t c h P e a k p r o s p e c t s at t h e h e a d of H a r d - t o - B e a t Canyon, T h e T i n t i c - D e l a w a r e m i n e i s on t h e c o n t a c t of t h e S h e e p r o ck s t o c k and P r e c a m b r i a n m e t a s e d i m e n t s in t h e h e a d of t h e m i d d le f o r k of A l b e r t E k k e r C a n y o n , W o r k i n g s t o t a l i n g 750 f e e t of d r i f t, r o u g h l y d e s c r i b e a D - s h a p e on one l e v e l . The p o r t a l p e n e t r a t es P r e c a m b r i a n q u a r t z i t e a p p r o x i m a t e l y 300 f e e t n o r t h of t h e g r a n i t e - m e t a s e d i m e n t c o n t a c t . The o r e , p r i n c i p a l l y p y r i t e , g a l e n a , and s p h a l e r i t e in q u a r t z g a n g u e , o c c u r s a s i r r e g u l a r m a s s e s a l o n g a f i s s u r e which m o r e o r l e s s p a r a l l e l s t h e t r e n d of t h e g r a n i t e c o n t a c t , A m a s s i v e h e m a t i t e g o s s a n m a r k s the s u r f a c e t r e n d of t he v e i n . S p e c u l a r i t e a i d s In t r a c i n g t h e m i n e r a l zone w e s t w a r d to the b o t t om of t h e left h a n d f o r k of A l b e r t E k k e r Canyon, t h e n c e t o w a rd t h e o l d P o r c u p i n e p r o s p e c t . One s m a l l p i l l a r in t h e m i n e a p p e a r e d1 t o b e of o r e g r a d e ; it was m a d e u p of g a l e n a and p y r i t e in a m a t r ix of s e r i c i t e. T h e I n d i a n a p o l i s m i n e i s n e a r t h e h e a d of t h e left h a n d f o r k of South P i n e C a n y o n , The w o r k i n g s t o t a l 310 f e e t and a r e i n c l i n e d along a v e i n which s t r i k e s S, 6 5 s E , The o r e i s s p e c u l a r i t e , g a l e n a , and s p h a l e r i t e with q u a r t z g a n g u e . The l o w e r m o s t w o r k i n g s c o n t a in s o m e p y r i t e r e p o r t e d to c o n t a i n up t o $30 in g o l d p e r t o n , P r e c a m b r i a n q u a r t z i t e and m i n o r a m o u n t s of s l a t e c o m p o s e the wall |
