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r-~,ll ~rr-~- -IJ;=, -77- ~J U /` IJ U The second unit of the Williams Fork Formation is comprised of the Middle sandstone, interbedded sandy shale, shale, coal and the massive Twentymile sandstone. The Middle sandstone contains sedimentary structures typical of a deltaic barrier island environment. The Middle sandstone is cross-bedded and contains fine-grained interbeds with clay drapes formed on cross-beds. Two mineable coal seams are above the Middle sandstone; the Hart seam and the "H" seam. The Twentymile sandstone lies at the top of this unit. It is a thick cross-bedded sandstone that averages 120 feet thick in the general area. This unit is composed of fine to medium-grained calcareous sandstone. The Middle sandstone and the Twentymile sandstone form resistant sandstone cliffs along the valley walls of the Yampa and Williams Fork Rivers. The third unit is referred to as the Upper Williams Fork Formation. It overlies the Twentymile sandstone and is composed primarily of 680 feet of complex interbedded sandstones, siltstones, sandy shales, shales and coats. The Eagle No. 9 undergroun4 coal mine and the Trapper surface coal mine are both presently mining coal seams in this unit. The proposed Sugarloaf Mine also proposes strip mining the coals of the Upper Williams Fork Formation. Nomenclature used for the coal seams in this unit at each mine, however, differ from mine-to-mine. The Eagle No. 9 Mine is in what Empire Energy Corporation labels the "P" seam. The "H", "I", "L", "Q"-rider, "q", "R"-rider, and "R" seams are being strip mined at the Trapper Mine. All of the coal seams being mined at the Trapper Mine are within the Upper Williams Fork Formation. Within the strata of the Upper Williams Fork Formation is a series of three massive sandstones; the White sandstones. The combined thicknesses of these sandstones is 350 to 450 feet. The stratlgraphic positions of the individual sandstones are, in ascending order, the first, second, and third (Utah International Inc. uses a reverse ordering). Separating each of the sandstone units is a thin series of shales and thin coals. The three sandstone units have similar fine to very fine-grained calcareous sandstone lithologies. The Eagle No. 9 Mine is overlain by the White sandstones. These sandstones are separated from the Eagle No. 9 workings by an average of 130 feet of interburden shales, siltstones, sandstones and coals. The White sandstones are stratigraphically located about 20-50 feet above the "H" coal seam, the uppermost seam to be recovered at the Trapper Mine (see Map M11-C of the Trapper Mine permit application). The White sandstone may be present at the proposed Sugarloaf Mine site. However, no attempt has been made to correlate the Upper Williams Fork Formation as of yet. Above the Mesaverde Group is the Lewis Shale, which is a 1,500 to 2,000 foot thick sequence of dark-gray to bluish, homogenous marine shale with several thin interbedde4 sandstones and calcareous concretions. The shale is bentonitic and swells with hydration. This formation is found primarily in depressions such as the center of the Round Bottom and Big Bottom synclines where this highly erosive unit remains as a remnant.