OCR Text |
Show sedimentary rock found at various points above or near high water elevation which protrude through the volcanic rocko These are indications of the uneven surface upon which the volcanic rock was lain. Drill holes indicate the volcanic rock to be several hundred feet in thickness near the center of the reservoir area. Near Hailstone Junction some of the volcanics are severely weathered and altered. This could result in minor slumping on steep slopes during proposed reservoir operation. Small slumps are now present along the left side of the proposed reservoir site due to alternation and failure of oversteepened sideslope erosion. A large slump or slide, located downstream of the potential left abutment, formed as a result of failure of the soft ashy agglomerate as the river oversteepened the side slope. The left abutment, about 400 feet upstream from the slide, would consist of competent, hard andesite rock. Faulting is present within the feature area as a result of uplift and forces related to intrusion of the large igneous stocks. Fault zones known and mapped by the mining companies cross the valley from the Mayflower mine on the west to the vicinity of the Park Premier shaft on the east of the valley. The Cottonwood fault is located above the right abutment site cutting into the reservoir upstream several hundred feet from the damsite axis. Other faults of much less magnitude than those mentioned are present. Geologic studies at this time have not defined these structures nor their significance to the design of the dam. These studies are continuing. There are several springs and seeps within and higher in elevation than the proposed reservoir elevation. All of these would be tributary to the reservoir„ A high and normal water table was found at the damsite and reservoir in all drill holes completed to date. Drilling and geologic studies are presently being performed by the Bureau of Reclamation to establish groundwater conditions along the reservoir area which would be in close proximity to the mining properties along the west side of the reservoir area. Data obtained to date indicate all groundwater, some of which is artesian, is tributary to the reservoir site and that the reservoir basin is water tight0 Maps and descriptions of geologic data for feasibility studies are found in the Bureau of Reclamation's feasibility Geologic Report, G- 255„ Local Geology-- Other Feature Sites Detailed geologic data are being collected on other feature sites in the Bonneville Basin portion of the Unit area. 120 |