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Mayo and Assoelafes, LC <br />• The geology of the West Elk lease area is shown on Figure 4 and Plate 1. Geologic cross- <br />sections through the mine lease area are shown in Figure 5. Bedrock formations in the West <br />Elk lease area are described below. <br />Mancos Shale <br />The Mancos Shale is the oldest formation exposed in the West Elk Mine area. It consists of <br />dark gray to buff shale approximately ?,000 to 3,000 feet thick. The Mancos Shale was <br />deposited in an open marine environment and is highly erodeable calcareous, gypsiferous, <br />and carbonaceous. <br />Mesaverde Formation <br />• The Mancos shale is overlain by [he Upper Cretaceous Mesaverde Formation. The <br />Mesaverde contains five stratigraphic units. These units are, in ascending stratigraphic order, <br />the basal Rollins Sandstone Member, the Lower Coal Member, the Upper Coal Member, the <br />Barren Member, and the Ohio Creek Member. The total thickness of the Mesaverde <br />Fommation is about 2,500 feet in the vicinity of the West Elk Mine. Each of the five units of <br />the Mesaverde Formation is described below. <br />Rollins Sandstone Member <br />The Rollitms Sandstone forms a prominent cliff beneath the Mesaverde Fommation in [he West <br />Elk area. The sandstone intertongues with the underlying Mancos Shale. It consists of white <br />to buff, well-sorted fine- to tmmediunm-grained sandstone. In the vicinity of the West Elk Mine, <br />• the Rollins Sandstone is fronm 150 to 300 feet thick. Althouglm the Rollins Sandstone is a <br />Characterization of Groundwater Systems in the Vicinity of the West Elk Mine, Somerset, Colorado <br />29 January 1999 <br />Page 13 <br />