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-26- 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 "B" (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 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. 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. Three coal horizons have been identified in the Upper Coal member, the "D" (Oliver) Horizon, the "E" (Hawk's Nest) horizon, and the "F" horizon. The "D" horizon occurs directly above the massive sandstone of the Lower Coal-Bearing member and contains three seams. This horizon is currently being mined in the Orchard Valley Mine, and is planned to be mined at the Hawk's Nest Mine. The "E" horizon occurs about 130 feet above the "D" horizon and contains two coal seams. This horizon is currently being mined at the Hawk's Nest Mine and at the Blue Ribbon Mine. It may be mined at the Mt. Gunnison Mine and at the Bear No. 3 Mine in the future. The "F" horizon contains two coal seams and presently is only mined at the Mt. Gunnison Mine. Coal seams of the "F" horizon do not exist to the north of the North Fork in thicknesses sufficient for mining. The Barren (Undifferentiated) member of the Mesa Verde Formation consists of up to 1,600 feet of terrestrial sedimentary rocks. This unit consists of fine-grained, buff-colored, lenticular sandstones, gray shales and thin lenticular coal beds. The sandstones predominate and are highly lenticular, discontinuous and of limited lateral extent in outcrop (Johnson, 1948). The Mesa Verde Formation is unconformably overlain by the Tertiary Age Rudy or Wasatch Formation. This formation consists of red to buff-colored shales, red sandstones, and red to gray conglomerates. The sediments of this formation are weathered volcanic rocks. The Ohio Creek conglomerate is the basal unit within the formation and is 100 to 200 feet thick. Igneous intrusive rocks exist within the North Fork Drainage Basin. A diorite plug about 1,000 feet in diameter outcrops along Hubbard Creek in the SE 1/4 of Section 7. This may represent the erosional remnants of a volcanic flow feeder. Sills have injected the Lower Coal-Bearing member, particularly the "B" and "C" seams. These sills consist of diorite and appear to have their source to the northwest of Terror Creek.