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i - 38 - i 1 ' 1 2.04.6 Geology Descr~i tion i 1, The coal in Sunlight Mine belongs to the Fairfield coal group which occurs in the C1 Bowie Shale A7ember of Williams Fork Formation. The group lies about 70 feet above the Rollins Sandstone which is a marker bed equivalent to the Trout Creek Sandstone j' elsewhere in Colorado. ,,,,~ The Bowie Shale Member of Williams Fork Formation contains two prominent ~ ' sandstone beds, termed the middle and upper sandstones, each approximately 100 feet f thick in the Sunlight area (Figure G.S, G.7 and G.S). The sandstones are tan to buff in l , weathered outcrop, quartzose, and normally fine to very fine in grain size and massive I' to thin-bedded. They commonly fine gradually downward through a transition zone of thinner beds until the section becomes entirely gray to brown shale. Because the beds I, dip at approximately a 100% grade, their areas of outcrop are small and the entire section is transected in only-a short distance horizontally. A stereo pair of aerial ' photographs covering the Sunlight Mine and vicinity (Figure G. 9) shows very well the ' l prominent dip of the bedrock strata in the area. Gray, vesicular basalt caps some of the mountains in the vicinity of Sunlight, but ~.' none of these basalt flow units are in proximity to or otherwise related to the Fairfield coal group at the Sunlight Aline (Figure G.6) ' Unconsolidated alluvial deposits, chiefly sand, gravel, and basalt cobbles and l boulders, occur along the narrow channel of Fourmile Creek upstream and downstream ' of the Sunlight Aline. AlonR.th~s a^tire reach of stream the alluvial deposits are mixed ~' with artificial fill material derived from construction of the paved road in the valley L ' and from coal mine wastes from earlier periods of mining. The valley deposits directly adjacent to the Sunli ht Aline are a mixture of road construction debris old coal mine g , wastes, old coal stockpiles, now eroded, and debris disrupted during construction of 1 " " the sediment pond in the valley. .+~ ~1 2 0