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erodible and unstable. Erosion and over- steepening of slopes in this formation produce the <br />numerous rock falls and landslides observed in the lower North Fork drainage basin. <br />The Mesaverde Formation conformably overlies the Mancos Shale. This formation consists of <br />approximately 2,300 feet of marine and terrestrial sedimentary rocks. The Mesaverde Formatioc <br />is the coal-bearing formation in the region and is divided into four main members -the Rollins <br />Sandstone, the Lower Coal Beazing (Bowie) member, the Upper Coal Bearing (Paonia) member, <br />and the Barren (Undifferentiated) member. <br />The Rollins Sandstone member is a 120- to 300-foot-thick, massive, cross-bedded, medium- to <br />fine-grained, buff to white sandstone. This sandstone is regionally extensive and resistant in <br />outcrop and forms prominent cliffs. This member is used regionally as a marker horizon to <br />define the top of the Mancos Shale and the bottom of the coal-bearing horizons. <br />The Lower Coal Bearing (Bowie) member consists of 260 to 350 feet of interbedded gray shales, <br />thin to thick lenticular beds ofbuff-colored, fine- to medium-grained sandstones, and coals. The <br />top of the member is usually capped by a massive buff-colored sandstone up to 90 feet in <br />thickness. This sandstone, however, appeazs not to be a single persistent bed, but is actually <br />several thick lenticular sandstones occurring at progressively lower stratigraphic horizons from <br />east to west. <br />Three coal beds exist in the Lower Coal Bearing member - the A (Old King) horizon, the B <br />(Somerset) horizon, and the C (Bear) horizon. The A horizon is immediately above the Rollins <br />sandstone and is not currently mined. The B horizon contains two coal seams and occurs about <br />20 to 120 feet above the Rollins sandstone. The C horizon contains one coal seam that occurs 50 <br />to 100 feet above the B horizon. <br />The Upper Coal Bearing (Paonia) member consists of 200 to 500 feet of gray shales, interbedded, <br />buff-colored, lenticulaz sandstones, and coals. The top of this member usually grades into a <br />massive, cliff-forming sandstone. However, like the similar sandstone at the top of the Lower <br />Coal member, this sandstone is not a single persistent bed. <br />Three coal horizons have been identified in the Upper Coal member - the D (Oliver) horizon, the <br />E (Hawk's Nest) horizon, and the F horizon. The D horizon occurs directly above the "massive" <br />sandstone of the Lower Coal Beazing member and contains three seams. This horizon was <br />mined in the Bowie No. 1 Mine. The E horizon occurs about 130 feet above the D horizon and <br />contains two coal seams. The F horizon contains two coal seams. Coal seams of the F horizon <br />do not exist to the north of the North Fork of the Gunnison River in thicknesses sufficient for <br />mining. <br />The Barren (Undifferentiated) member of the Mesaverde Formation consists of up to 1,500 feet <br />of terrestrial sedimentary rocks. This unit consists offine-grained, buff-colored, lenticular <br />sandstones, gray shales and thin, lenticular coal beds. The sandstones predominate and are <br />highly lenticular, discontinuous and of limited lateral extent in outcrop. <br />13 <br />