2001-12-11_PERMIT FILE - C1980005 (4)

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State Reg. GEOLOGY PHYSIOGRAPHY The Seneca II Mine is located in the structurally complex southeastern syncline extension of the Washakie structural basin in the Wyoming Basin Physiographic Province of southcentral Wyoming and northern Colorado (Bass, et. al, 1955). Having a relief of approximately 1,900 feet, the rugged rolling topography of the Seneca II Mine Permit area is typical of the surrounding area. Chavez Peak (elevation 8106 feet) marks the highest point within the permit boundary and Grassy Creek (elevation = 6200 feet) is the lowest point. For the most part, the Seneca II Mine is drained by Grassy Creek. How- ever, asmall portion of the permit area is drained by Fish Creek to the southeast. Both Grassy Creek and Fish Creek drain into the Yampa • River which is part of the upper Colorado River drainage basin. The drainage area is described in more detail- in the hydrology section (Tab 7) of this report. Prominent physiographic features in the direct vicinity of the Seneca II Mine include the ruggedly rolling Williams Fork Mountains to the south- west, the more gentle rolling Twentymile and Eckman Parks to the east and south, respectively, the Sage Creek drainage basin to the west and the Yampa River Floodplain to the north. In addition, cliffs of sandstone lie on both sides of Grassy Creek directly to the north of the property. These prominent geomorphological features are deeply incised by ephemeral subdrainage basins of Grassy Creek. In addition, the cliffs are ' typical of the erosion resistant Twentymile sandstone. STRATIGRAPHIC RELATIONSHIP Approximately 13,000 feet of Upper Cretaceous and Tertiary sandstones, . shales, and coal of the Seneca II Mine area represent a variety of deposi- tional environs. A brief depositional history from late Mesozoic time to present may be given as follows: 6-I Revised 5/27/1981