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-2~- The Mesaverde Formation is of Late Cretaceous Age and conformably overlies the Mancos Shale. This formation consists of approximately 2,300 feet of marine and terrestrial sedimentary rocks. The hlesaverde Formation is the coal-bearing formation in the region and is divided into four main members; the Rollins sandstone, the Lower Coal Bearing (Bowie) member, the Upper Coal Bearing (Paonia) member, and the Barren (Undifferentiated) member (Johnson, 1948). The Rollins sandstone member is a 120 to 200 foot thick, massive, cross-bedded, medium to fine-grained, buff to white sandstone. This sandstone is regionally extensive and resistant in outcrop and forms prominent cliffs. This member is used regionally as a marker horizon to define the top of the Mancos Shale and the bottom of the coal-bearing horizons. The Lower Coal Bearing (bowie) member consists of 260 to 350 feet of interbedded gray shales, thin to thick lenticular beds of buff-colored, fine- to medium-grained sandstones, and coals. The top of the member is usually capped by a massive buff-colored sandstone up to 90 feet in thickness. This sandstone, however, appears not to be a single persistent bed, but is actually several thick lenticular sandstones occurring at progressively lower stratigraphic horizons from east to west. Three coal horizons exist in the Lower Coal-Bearing member; the "A" (Old King) horizon, the "8" (Somerset) horizon, and the "C" (Bear) horizon. The "A" horizon is immediately above the Rollins sandstone and is not currently mined. The "B" horizon contains two coal seams and occurs about 20 to 120 feet above the Rollins sandstone. This horizon is presently mined by U. S. Steel at the Somerset Mine and may be mined at the Mt. Gunnison Mine. The "C" horizon contains one coal seam that occurs 50 to 100 feet above the "B" horizon. This horizon has been mined at U.S. Steel's Elk Creek Mine and the Bear No. 1 and 2 Mines, and is currently mined at the Bear No. 3 Mine. It may be mined at the Mt. Gunnison Mine in the future. The Upper Coal-Bearing (Paonia) member consists of 200 to 500 feet of gray shales; interbedded, buff-colored, lenticular sandstones; and coals. The top of this member is generally considered to be capped by a massive, cliff-forming sandstone. However, like the similar sandstone at the top of the Lower Coal member, this sandstone is not a single persistent bed. Drill hole data for both the Mt. Gunnison and the Somerset life-of-mine areas show this sandstone unit to occur as several lenticular sandstones at slightly different stratigraphic horizons.