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Mayo and Assoclafes, LC <br />• Ohio Creek Member <br />The Ohio Creek Member is the uppermost member of the Mesaverde Formation. It is 700 <br />feet thick and consists primarily of interbedded sandstone, mudstone, and shale. The <br />sandstones range from a few feet to nwre than 100 feet in thickness and generally have a <br />lenticular shape. Sandstones are typically fine to coarse grained, and locally are <br />conglomeratic. The Ohio Creek Member is not a hydrogeologically significant rock unit in <br />the mine lease area because it only occurs in limited areas. <br />Wasatch Formation <br />The Wasatch Formation is of Tertiary age and lies unconformably atop the Upper Cretaceous <br />Mesaverde Fornation. The Wasatch Formation is only exposed in the eastenunost portions <br />• of the West Elk Mine lease area where it caps the highest mesas. On West Flatiron Mesa, the <br />Wasatch Formation is made up of brownish-gray to reddish mudstone and its characteristic <br />basal conglomerate of sandstone, chert, and volcanic rocks. The Wasatch Formation is not of <br />hydrogeologic significance because the it only occurs in limited areas in the mine lease area. <br />Tertiary Igneous Intrusive Rocks <br />South and east of the West Elk Mine lease area, igneous intntsive rocks of Tertiary age form <br />the laccoliths of Mount Gunnison and West Beckwith Peak. Locally, the weathering <br />products of the Tertiary intrusive rocks and rocks from the Wasatch Fornation cover the <br />Ban•en and Ohio Creek Members of the Mesaverde Formation. <br />• <br />Characterization of Groundwater Systems in the Vicinity of the West Elk Mme, Somerset, Colorado <br />29 January 1999 <br />Page 20 <br />