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member of the fles Formation and the Tv+enty-mile sandstone member of the '+li lliams Fork Formation. The upper coal group includes the coal horizons of the Williams Fork Formation above the Trventy-mile sandstone member. It is the coal horizons of the middle coal group [hat are of economical interest in the area. Hiddle Coal Grouo The middle coal group of the Mesaverde Group occurs in a 400-foot sequence of sandstone, sandy shale, and shale between Che Trout Creek and Twenty mile sandstone members. 'Within this group, in ascending order, is the Wolf Creek, Sage Creek, Wadge, and Lennox coal seams (Figure 2). The lorvermost seam, the Wolf Creek, varies in thickness from 13.0 to 22.0 feet and, in places, exhibits a shale parting caused by an increase fn water velocity into the paludal environment. Above the Wolf Creek coal seam is a sequence of sandstone, sandy shale, and shale approximately 100 feet thick. Overlying this interval is [he Saae Creek coal seam. The Sage Creek coal ranges in thickness from about five feet [o one foot or less. Separating the Sage Creek and Wadge coal seams is a sequence of predominantly Sandstone interbedded with sandy shale, Shale, and thin coal beds. This 50-foot thick strata, although dominated by sandstone, exhibits some facies change, lensing, and interbedding due to variations in depositional environments. The Wadge coal seam possesses the most uniform lateral continuity and quality of the four coal seams in [he middle coal group. The -ladge seam varies from about 7.5 to 13.0 feet in thickness and, like the Wolf Creek seam, may contain a shale parting. The Wadge coal seam is separated from the uppermost coal, the Lennox, by a 50-foot thick sequence consisting of sandstone interbedded with sandy shale and shale, This strata is very similar to that underlying thn Wadge seam; however, the shales and sandy shales appear to comprise more of the strata above than below the Wadge. The Lennox coal seam varies from 2.0 to 6.0 feet thick, but may be absent due to erosion. The material above the Lennox coal seam consists of sequences of sandstone, sandy shale, and shale.