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4.1.1.3 Stratigraphy Exhibit 3 is a generalized geologic column of the area. All bedrock ex- posed in the Hayden Gulch area is Upper Cretaceous. The youngest is the Lewis shale, followed by the Willimas Fork and Iles formations of the Mesaverde group, and the Mancos Shale. Since bedrock older than the h1ancos shale is far below the mining zone, it will not be considered here. The Lewis shale consists mainly of a dark-gray, homogeneous marine shale. It is comformable with the underlying Willimas Fork Formation. The contact with the Williams Fork is not sharply defined, and therefore it was arbi- trarily placed at the top of the beds, which consist mainly of sandstone, sandy shale, and coal as differentiated from overlying beds of mainly gray shale (Bass et. al., 1955). The Lewis shale is found immediately north and east of the site. The Willimas Fork formation consists of a sequence of sandstones,. silt- stones, mudstones, shales, and coals lying between the Lewis .Shale and • the Trout Creek Sandstone. Included are a lower unit and an upper unit separated by the ledge-forming Twenty Mile Sandstone. The upper unit of the Williams Fork is roughly 600 ft. thick and includes the five coal beds within the mining zone of the proposed Hayden Gulch Mine as well as several beds below the zone. The coals are separated by siltstones, mudstones, and sandstones. At the base of the upper unit is the massive, well-sorted, medium grained, white to tan Twenty Mile Sandstone. The Twenty Mile is about 100 ft. thick in the mine area and forms distinctive ledges below the southern end of the mine site. Below the Willimas Fork is the Iles formation. It is taped by the 100 ft. thick Trout Creek Sandstone, which is similar in composition to the Twenty Mile. The Trout Creek forms white ledges about 1 mi. to the south of the 6 ,. ~ I ~ ~ ~ - .;~~