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Mesaverde Formation is composed of four members which are, in order of decreasing age, the <br />Rollins Sandstone, the Lower and Upper Coal members and the Barren member. <br />Minor faulting of limited vertical displacement has been observed in other nearby mines. <br />However, in the Bowie No. 1 Mine, a fault with a displacement of fifty (50) feet was encountered <br />during mining, and drill-hole data indicates the presence of other faults in the life -of -mine area <br />with similar displacements. The faults which have been encountered in these mines tend to be <br />high -angle, normal faults. <br />The steep slopes of the stream valleys and the instability of the rock strata in the North Fork <br />drainage basin have contributed to numerous landslides, mud flows and rock falls. These mass <br />wasting features have been mapped by W.R Junge of the Colorado Geological Survey and <br />published as an open file report entitled "Geologic Hazards, North Fork Gunnison River Valley, <br />Delta and Gunnison Counties, Colorado." <br />Geologic units exposed in the North Fork Drainage Basin consist of Late Cretaceous to Early <br />Tertiary Age sedimentary strata, Tertiary Age igneous intrusives, and Quaternary Age alluvial and <br />colluvial deposits. The units of the Late Cretaceous in the general area are described below in <br />ascending order. A stratigraphic column representing the geology of the coal member of the <br />Mesaverde Formation in the permit area can be found on Map 2-10, Volume 2. <br />The Mancos Shale is the oldest formation exposed in the region. This unit is composed of over <br />4,000 feet of gray marine shales and minor interbedded buff sandstones. This unit is highly <br />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 Formation <br />is the coal -bearing formation in the region and is divided into four main members - the Rollins <br />Sandstone, the Lower Coal Bearing (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 define <br />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 of buff -colored, fine- to medium -grained sandstones, and coals. The <br />top ofthe member is usually cappedby a massive buff -colored sandstone up to 90 feet in thickness. <br />This sandstone, however, appears not to be a single persistent bed, but is actually several thick <br />lenticular sandstones occurring at progressively lower stratigraphic horizons from 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 />