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- 5 - <br />level valley bottom which contains the North Fork of the <br />Gunnison River. <br />The elevations of the bench are between approximately <br />6260 and 6310 feet. The existing surface is flat to gently <br />sloping. <br />2.2 GEOLOGY <br />The geology of the area has been described in reports <br />prepared by others; the bedrock at the site is comprised of <br />the Cretaceous Mesa Verde Formation. The formation consists of <br />shales (in some boring logs and reports, shales are classi- <br />fied as claystones), siltstones, and sandstones, with inter- <br />bedded coal. The formation is close to horizontally strati- <br />fied with dips of three to five degrees to the north-north- <br />east. <br />Distinct benches on the site (lower and upper bench) are <br />an important morphologic feature; their origin has not been <br />satisfactorily explained but very probably, they were caused <br />by selective stream erosion. <br />The lower bench is covered by a layer of soils, probably <br />of colluvial origin. The thickness of the soil cover is not <br />well defined; IECO (1976) indicated soil thickness on the <br />order of 35 to 75 feet. Woodward-Clyde (1978) questioned their <br />findings and indicated that the thickness may be much less <br />(soils might comprise weathered rock). Chen ~ Ass. (1980) <br />drilled and sampled a number of borings within the area of the <br />lower bench to a depth of 25 feet without ever identifying <br />bedrock. <br />~eoanoao conw~m+c, iNC. <br />