| OCR Text |
Show easterly to northeasterly parallel to the mountain front0 A general geology location map of the Uinta Basin portion of the Bonneville Unit is presented in Figure B- l. Overburden materials vary considerably in physical properties and in thickness. There are deposits of glacial debris at higher elevations with alluvial fans, slopewash, and glacial outwash at lower elevations. Landslides are common along the mountainfront, some would be near Unit features„ A large landslide is known to exist in the proposed area of the outlet portal of Stillwater Tunnel where large masses of earth and rock have slumped several hundred feet. The proposed portal site was located to minimize involvement with this slide and assure complete safety of the feature„ Another major slide is located downstream from Currant Creek damsite. This is considered an active slide, but is removed from the feature area. Uplift of the Uinta Mountains was accompanied by major and minor faulting, folding, or isostatic adjustment. This resulted in many small local flexures or structures paralleling the major uplift. The South Flank Fault, which extends along the entire south flank of the uplift, and numerous smaller faults and structures would be encountered by the aqueduct. Detailed field geologic mapping and study of the South Flank Fault by the Bureau of Reclamation has revealed no evidence that this fault is active. Research of all available geologic literature on the subject also confirms this conclusion. Upper Stillwater damsite would be in a wide gorge cut in the Uinta Mountain quartzite by glacial scour„ Heavy accumulation of talus rock is found at the base of steep rock slopes on each proposed abutmento On the basis of foundation drilling and exploration conducted by the Bureau of Reclamation, the foundation was found competent to support the damc Water table elevations in the proposed reservoir basin indicate favorable water- holding capability. Streamflow measurements taken at the proposed site of the Upper Stillwater Dam and about 5 miles below the proposed damsite indicate that flow losses periodically occur between these two points. At the same time, long- term measurements taken downstream about 8 miles, near the Forest- Indian Boundary, indicate that significant stream gains always occur„ Because this portion of Rock Creek is situated in the South Flank Fault Zone it is apparent that the stream flow pattern is being affected by local geological characteristics. The possible significance of this fault is discussed in Section C. 117 |
