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• approximately 200 to 850 feet in thickness throughout the region. Some <br />of the sandstones are quite massive, resembling the Twent~~nile sandstone <br />members. The actual number of coal beds within the Mesaverde Group <br />varies from area to area and may range from one to more than several. <br />One of the workable coal seams within this group is called the Dry Creek <br />coal bed and is situated about 400 feet above the Twentymile sandstone <br />member. <br />The Lewis shale conformably overlies the Mesaverde Group and, like the <br />upper unit of the Williams Fork Formation, is highly variable in <br />`_hickness. It is principally a homogenous marine shale. It tends to be <br />more sandy in the upper portion of the formation and may contain a few <br />lenticular sandstone layers. <br />The youngest Cretaceous rock formation exposed in the area is the Lance <br />Formation. It conformably overlies the Lewis shale and is about 1,000 <br />to 1,500 feet thick. The Lance Formation is comprised of interbedded <br />• shale, sandy shale, sandstone, and coal. Some of the sandstone layers <br />can be rather thick (about 100 feet). The only coal bed present in the <br />Lance Formation which is of any economic significance is the Kimberly <br />coal bed which has been found to be as thick as 14 feet in some areas. <br />The Fort Union Formation of Tertiary age lies above the Lance Formation. <br />It consists of interbedded sandstone, shales, and coal deposited during <br />the Paleocene epoch and is approximately 1,400 feet thick (Bass et al., <br />1955). Compared to the Lance Formation, the sandstones are coarser, the <br />shales are lighter gray in color and there are more coal layers. The <br />thickest regional coal seam present in the Fort Union Forma*.ion is the <br />Seymour Coal. <br />The Wasatch Formation of Eocene age unconformably overlies the Fort <br />Union Formation. It is comprised primarily of fresh water stream-laid <br />sandstone and shale deposits. Unconsolidated alluvial, terrace, and <br />surficial deposits of Quaternary age overlie the '.Jasatch Formation in <br />• some areas, particularly along larger streams. <br />2.04.6-5 <br />