| Description |
The Sheeprock Range, Tooele and Juab Counties, Utah, is composed chiefly of consolidated sedimentary rocks of Precambrian and Paleozoic age. Several areas of both intrusive and extrusive rocks are present. Unconsolidated sediments related to late Tertiary and Quaternary episodes cover much of the flanks of the range as pediment gravels, lake deposits, and alluvium. Nearly 11,000 feet of Precambrian metasediments, largely slates and quartzites similar to late Precambrian formations in central and western Utah, crop out in the central part of the area. Tillites similar to those found locally in the Wasatch Mountains are the thickest and most distinctive of the Precambrian rocks. Twenty-seven formations having a combined thickness of approximately 20,000 feet represent the Paleozoic era and include rocks of all Paleozoic periods excepting (?) Permian. Over 80 percent of the Paleozoic rocks are of marine origin, the remainder are continental-interior-shelf and shoreline deposits. Limestone, dolomite, quartzite, and shale typical of miogeosynclinal environment constitute the Paleozoic rock types. Excepting minor hiatuses, continuous sedimentation prevailed from Precambrian into Pennsylvanian. All formations were strongly folded and broken by thrust faults during the Laramide orogeny. Rock units necessary for precise relative dating of Laramide and later orogenic events are not present in the Sheeprock Range, but the relationships of preserved structures permit the establishment of a sequence of deformational phases as follows: (1) Cedar Hills orogeny(?) - Mid-Cretaceous phase, (2) Early Laramide orogeny - Montana phase, (3) Mid-Laramide orogeny (?) - Paleocene phase, (4) Late Laramide orogeny, and (5) Basin and Range phase. Structures formed during these phases include folds, thrust faults and imbrications, and normal faults, and the structures of each successive phase are superposed upon those of earlier phases. Igneous activity which began in early Tertiary and continued into Miocene formed granitic and monzonitic intrusions and extensive rhyolitic and andesitic flows. A single small area of basalt of undetermined age is present. The resulting structure of the Sheeprock Range is essentially a northward-dipping homocline modified by several folds, major thrusts, and intrusions. Normal faulting of the Basin and Range orogenic phase, concomitant with and following the igneous activity, affected both Tertiary and older rocks and is primarily responsible for the present topography and out¬ line of the Sheeprock Range. Lake Bonneville shoreline features along the western part of the area and a questionable morainal deposit at the mouth of North Oak Brush Canyon represent Pleistocene events. Mineral deposits fall into two major groups: (1) deposits associated with the West Tintic monzonite cutting Precambrian and Paleozoic rocks have yielded minor quantities of commercial ores of lead, zinc, silver, gold, and tungsten; (2) deposits associated with the Sheeprock granite have yielded ores and protores of beryllium, lead, silver, tungsten, thorium, and uranium, but none of these has achieved commercial significance. |
