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I I I I I I I I I I I I I I I I I I I ;)[l1~38 4. PROJECT GEOLOGY The defi niti on of the project area for the purpose of geologic mappi ng is those areas whi ch woul d be impacted, or are adj acent to areas that woul d be impacted, by construction of one of the dams studied. Plates 4 through 8 are geol ogi c maps prepared at a scal e of one inch to 2,000 feet. The maps on Pl ates 4 through 6 cover the eastern, or upstream part of the project area. The easternmost 1 imi tis about three mi 1 es upstream of Buford, where the diversi on facil i ty for the Lake Avery enl argement woul d be located. The mapped area extends west to about one half mile below the Highland Ditch Headgate. Pl ates 7 and 8 cover the area from the state hi ghway bri dge just downstream of Meeker, west to Smith Gulch whi ch is adj acent to the furthest downstream site studied. 4.1 Bedrock Stratigraphy Eagle Valley-Minturn Formations (PPem) The 01 dest rocks exposed in the mapped area are of Pennsyl vani an-Penni an age and crop out along the North and South Forks of the White River and along Miller Creek where the streams cut into the northwest side of the White River Uplift. The rocks are yellow to gray sandstones, shales, and carbonate reefs of the Minturn Formation intertongued with white anhydrite and gypsum of the Eagle Valley Evaporite facies. The Minturn Formation is locally transitional with gray and reddish-gray siltstones, shales, and sandstones of the Eagle Vall ey Formati on. The terrai n is characteri zed by steep uneven slopes wi th small deeply cut stream drai nages. Where the Eagl e Vall ey Evapori te faci es occurs, the ground surface is frequently poclcmarked with sink holes caused by the coll apse of subsurface sol uti on cavi ti es. These units were mapped as "undifferentiated" in the field, as contacts were irregular and poorly defined. The thickness of this sequence was not determined; the literature indicates it to be in excess of 3,000 ft. Maroon Formation (PPm) Conformably overlyi ng the Mi nturn and Eagl e Vall ey Formati ons are red beds about 4,000 feet in thickness, the oldest of which is the Maroon Formation. 4-1