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Geology -Rules 2.04.5 and 2.04.6(21 <br />Information on local and regional geology can be found on pages I S to 26 of Section 2.04.6 of <br />Volume 1. Maps 2-1, 2-2, 2-7, 2-8, 2-11, 2-12 and 6A-8 identify pertinent geologic features. <br />Waste rock geochemical analyses can be found in Volume 6A. <br />BRL has mined the D seam of the Upper Coal member of the Mesaverde Formation. The seam <br />ranges in thickness from 2 to 21 feet in the permit area, with one split ranging in thickness from <br />15 1/2 feet to several inches. The coal dips 4N to 7N to the northeast. Two high-angle, normal <br />fault zones are found in the area with displacement ranging between I and 50 feet (Map 2-8). <br />The earliest fault system trends N65NE and dips 70N to 80N with displacements of 2 to 6 feet. <br />The other fault system trends N35NW and dip 70N to 80N to the northeast. The geology is <br />further modified in the northeast corner of Lease C-37210 where coked coal gives evidence of <br />igneous activity associated with the Miocene Iron Point pluton. <br />The Somerset Coal Field lies on the southeast margin of the Piceance Basin and just south of <br />Grand Mesa. The sedimentary strata exposed in the Somerset Coal Field dip at 3N to SN to the <br />north and northeast, and range in age from late Cretaceous to early Tertiary. <br />Coal is produced from the Mesaverde Formation, a 2500-foot-thick sequence of sandstone, shale <br />and coals overlain by the Ohio Creek conglomerate and underlain by the Mancos Shale (Figure <br />2). The Mesaverde Formation is composed of four members, which are, in order of decreasing <br />age, the Rollins Sandstone, the Lower and Upper Coal members and the Barren member. <br />Minor faulting of limited vertical displacement has been observed in other neazby 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 <br />and colluvial deposits. The units of the Late Cretaceous in the general area aze described below <br />in 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 2-1 Q Volume 2, and is found in <br />this document as Figure 3. <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 />12 <br />