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<br />Stratigraphy: ~ <br />The Hesperus area, located on the Northwestern flank of the San Juan <br />Basin, contains rocks of Quaternary and Cretaceous age. The Quaternary sedi- <br />ments are confined to the valley bottoms ar.d in particular the La Plata River <br />valley along the Eastern portion of the area. These deposits are primarily <br />poorly consolidated gravels. <br />The Cretaceous rocks exposed in the project area consist of Mancos <br />Shale, the coal bearing Mesa Verde Group, and the Lewis Shale. The Mancos and <br />Lewis shales are of marine origin and the sediments of the Mesa Verde Group are <br />of nonmarine origin. The Menefee Formation; the middle member of the Mesa <br />Verde Group, is the primary coal bearing formation. <br />Mancos Shale: The Mancos Shale conformably overlies the Dakota sand- <br />stone and is approximately 2,000 feet thick. It consists of dark gray to black <br />shale and silty-sandy shale with small amounts of dark gray argillaceous lime- <br />stone in lenses and concretions which weather to a bright yellow-brown color. <br />Point Lookout Sandstone: The Point Lookout Sandstone is the basal <br />member of the Mesa Verde Group in the Iesperus area. In this section, the <br />Point LooY.out Sandstone is divided into two members: a lower member made up of <br />thin sandstone beds with interbedded shale that compromises a transitional <br />sequence above t'ne Mancos Shale; and an upper massive sandstone member consist- <br />ing of thick, massive beds of even ter.tured, medium-y rained sandstone that is <br />cliff forming. <br />The Point Lookout Sandstone is reported to maintain a rather uniform <br />thickness of about 400 feet across the Hesperus area, but the sandstone beds at <br />any given horizon become progressively finer grained Eastward and the lower <br />member thickens at the expense of the massive sandstone member. In the project <br />area, the massive sandstone member of marine origin is about 700 feet thick and <br />the lower transitional member is about 300 feet thick. <br />Menefee Formation: The Menefee formation is the middle member of the <br />Mesa Verde Group and consists of the complex assemblage of lenticular cross- <br />bedded sandstone beds, gray, Brown, and black shales, and coal beds. The <br />