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The Mancos Shale consists of over 5,300 feet of marine shale, with minor interbeds of sandstone and Limestone. - The Iles Formation overlies the Mancos Formation. The strata consist of a ma medium-to-fine-grained sandstones, the sandstones. The Trout Creek sandstone permit boundary along the valley walls River. The Trout Creek sandstone is a Iles Formation. Shale and underlies the Williams Fork ssive marine shale between two massive Tow Creek and the Trout Creek outcrops in the southern part of the of the Yampa River and Williams Fork regional marker bed at the top of the The Williams Fork Formation overlies the Trout Creek sandstone of the Iles Formation (See Figure 4). The Williams Fork Formation consists of massive sandstones and shales; and interbedded and lenticular shales, siltstones, sandstones and coals. The Twentymile sandstone is a massive sandstone and is used as a key marker bed within the region. The Middle sandstone and White sandstone are two significant members of the Williams Fork Formation which are laterally extensive in the permit and adjacent areas. Several coal seams are located within the Williams Fork Formation which are mineable by underground methods. These include the "C", "E", "F", "H" and "P" seams, and the Hart seam (See Figure 4). The "F" seam is being mined in the Eagle No. 5 mine and the "P" seam was mined at the Eagle No. 9 Mine between 1977 and 1985. The proposed No. 6 Mine will be in the "E" seam. Previous mining within the permit area includes the Fields Mine which operated in the "E" seam during the 1930'5; the Wise Mine and Wise Hill No. 2 operated in the "C" seam during the 1940's and 1950'5. Previous mining operations in the Hart seam were the !eo White and Baker Mines during the 1930'5 and the Wise Hill Nos. 3 and 4 in the 1970'5. Surface Water Hydrology There are two (2) major northwestern Colorado rivers which intersect the permit area. These are the Yampa and Williams Fork Rivers. The Yampa River runs from north to south through the permit area, while the Williams Fork River runs from south to north and intersects the Yampa River just north of the mine facilities area. , The northern portion of the permit area is dominated by the Big Bottom alluvium, while the southern and eastern portions of the permit area are dominated by the Williams Fork Mountains and the river beds of the Yampa and Williams Fork Rivers, Both rivers depend primarily on snowmelt for their flow. Ground water discharge contributes to the base flow in the late summer months. Both the Yampa and Williams Fork Rivers have deeply incised valleys at their confluence due to down-cutting in the resistant sequence of sandstones in this area. The broad valley floors of Big and Round Bottoms resulted from the erosion of the less resistant rock strata of the Lewis Shale. -8-