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Topography. Within the Seneca II-W permit area, elevations range from approximately 6,385 <br />to 8,350 feet, slopes range from about 2 percent to nearly 100 percent in some areas, and <br />many of the drainages are deeply incised. Prominent ledges are formed by the Twentymile and <br />Trout Creek sandstones as well as by lesser sandstone units. The Twentymile sandstone ledge <br />is found to the west of the permit area and the Trout Creek sandstone ledge is found along the <br />eastern boundary of the permit area (Exhibit 6-11. <br />Two drainages, Hubberson Gulcli and an unnamed tributary of Dry Creek, run through the <br />permit area. Sage Creek lies to the east of the permit area. The fluvial geomorphology of the <br />permit area is detailed in Tab 7. <br />Stratigraphy. The oldest formation that outcrops within the Seneca II-W permit area is the Iles <br />Formation of the Mesaverde Group. The Iles Formation of Late Cretaceous age outcrops along <br />the easternmost boundary of thin permit area. It is capped by the Trout Creek sandstone <br />member, aline-grained, glauconific sandstone interbedded with carbonaceous shale s':ringers. <br />Along the eastern side of the permit area, the Trout Creek sandstone is approximately 100 feet <br />in thickness. The Trout Creek sandstone was deposited in a surf zone and near shore <br />environment (Gaffke, 19791. The rocks underlying the Trout Creek sandstone consist of <br />alternating beds of shales, sandstones, and thin coals. The coal beds are part of the lower coal <br />group of the Mesaverde Group an~i range in thickness from approximately 0.5 feet to 2.0 feet. <br />These underlying rocks outcrop immediately to the east of the Trout Creek sandstone or,~tcrop. • <br />The Williams Fork Formation overlies the Trout Creek sandstone and outcrops throughout most <br />of the lease area. The lowermost unit of the Williams Fork Formation contains the coal beds <br />that are of interest et the Seneca II-W Mine site. These coal beds are part of the middle coal <br />group of the Mesaverde Group; the Wolf Creek coal is the lowest coal bed in the middle coal <br />group (Figure 6-21. The Wolf Creak bed, which outcrops in the Southeastern portion of permit <br />area, is divided by partings into an upper Wolf Creek and a lower Wolf Creek. The upper seam <br />is about 7.5 feet thick, and is separated from the lower seam by a 3-foot interval of shale, <br />sandstone, and siltstone. The lower seam is approximately 16 feet thick and is underlain by <br />fine-grained sandstones, shales, mudstones, and thin coals (Gaffke, 19791• The Wol'I Creek <br />coal formed from peat deposited in a swamp environment. <br />• <br />6 Revised g/98 <br />