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Dakota Sandstone. The Dakota Sandstone consists of 100 to 150 feet of <br />hard gray to buff sandstone, locally quartzitic. It forms strike <br />ridges along the Grand Hogback. <br />Mancos Shale. The Mancos Shale forms strike valleys along the Grand <br />Hogback. It consists of two members of marine shale separated by a <br />limestone member and is at least 4,000 feet thick in the mine area. <br />Mesaverde Group. The Mesaverde Group comformably overlies the Mancos <br />Shale and is at least 4,000 feet thick, consisting of interbedded and <br />lenticular sandstone, shale, siltstone, and coal beds. In ascending <br />order, it contains (1) the Rollins sandstone member, (2) the Bowie <br />(coal-bearing) member, (3) the Paonia (coal-bearing) member, and (4) <br />the Upper (non-coal-bearing) member. The Rollins sandstone is part of <br />the Iles Formation, and the upper three members belong to the Williams <br />fork Formation (Figure 3.5.1-1). <br />The Rollins sandstone ranges from 80 to 120 feet thick. It consists <br />• of fine to medium-grained grayish-white sandstone that weathers to <br />light buff. The contact with the underlying Mancos Shale is tran- <br />sitional, but the top is generally well defined and easily mapped. <br />The Bowie member is about 850 feet thick and consists of four general <br />units. They are in ascending order: (1) a coal-bearing shale unit <br />420 to 480 feet thick (contains the A, R, and C seams), (2) a <br />sandstone unit (Middle sandstone) 50 to 100 feet thick which is simi- <br />lar to the Rollins sandstone, (3) a shale unit (about 150 feet thick) <br />which contains thin, presently non-commercial, coal seams in the south <br />end of the area, and (4j an Upper sandstone unit 60 to 100 feet thick. <br />• <br />3-21 <br />