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-19- The Mancos Shale is a thick (approximately 5,000 ft.) homogeneous light-gray to dark-gray fossiliferous marine shale with interbedded sandstone and limestone beds and is the oldest unit exposed in the area. The sandstones are generally thin bedded, fine grained, tan, and fossiliferous, and form resistant ledges in the basal and upper parts of the formation. The overall area occupied by the Mancos Shale is characterized Dy rolling hummocky topography. The Mesaverde Group is approximately 3,000 feet thick and conformably overlies the Mancos Shale. It consists of the Iles Formation and Williams Fork Formation. The Iles Formation is the lower unit and is approximately 1,500 ft. thick. It consists of interbedded light-brown to white, massive, fine-grained, ledge-forming sandstones, brown to black carbonaceous shale, sandy shale and coal beds.The coal beds are assigned to the lower coal group (Figure 4) of the Mesaverde, and are distributed throughout the middle and upper parts of the formation. Four persistent sandstone beds occur within the Iles Formation. They are: 1) the Tow Creek sandstone member at the base, 2) a double ledge-forming sandstone sequence 400 feet or more above the base, 3) a light-gray sandstone sequence of variable composition associated with the upper (No. 3) coals of the lower group situated about 900 to 1,000 feet above the base, and 4) the Trout Creek sandstone member which caps the formation. The Trout Creek sandstone is a 50 to 100 foot thick, light-brown to light-gray, fine-grained, massive sandstone. Many thin coals are present in the Iles formation, but the major coals are the Pinnacle (No. 2) and the Blacksmith. The Pinnacle splits frequently into as many as 4 minable coals. These overlie the Blacksmith coal by 100 to 150 feet. Two mines currently mine these coals in different synclinal basins. The Grassy Gap Mine and the Apex No. 2 Mine. The upper unit of the Mesaverde Group is the Williams Fork Formation which is approximately 1,000 to 2,000 feet thick and includes all beds between the top of the Trout Creek Sandstone Member and the base of the overlying Lewis Shale. The formation is conformable to its base and top, and it is divided into three units, the lower, middle and upper units. The lower unit is about 1,000 feet thick, consisting of shale, thin sandstone beds, sandy shale and several coal beds of the middle coal group. The middle coal group contains the coal seams of economic importance in this area. In ascending order they are the Wolf Creek, Wadge and Lennox coals. The extremely poor lateral continuity of the Wolf Creek and Lennox coals in the area of the Foidel Creek Mine make them unmineable. The middle unit of the Williams Fork Formation includes a massive, white, cross-bedded, cliff-forming sandstone about 100 to 200 feet thick, called the Twentymile Sandstone Member. The upper units of the Williams Fork Formation consist of interbedded sandstone, sandy shale, shale, sandstone and several thin coal beds of the upper coal group.