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Geology - Rules 2.04.5 and 2.04.6(2) <br />Information on local and regional geology can be found on pages 15 to 26 of Section 2.04.6 of Volume 1. <br />Maps;2-1, 2-2, 2-7, 2-8, 2-11, 2-12 and 6A-8 identify pertinent geologic features. Waste rock geochemical <br />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 ranges in <br />thickness from 2 to 21 feet in the permit area, with one split ranging in thickness from 15 1/2 feet to <br />several inches. The coal dips 4N to 7N to the northeast. Two high-angle, normal fault zones are found in <br />the area with displacement ranging between 1 and 50 feet (Map 2-8). The earliest fault system trends <br />N6514E and dips 70N to 80N with displacements of 2 to 6 feet. The other fault system trends N35NW and <br />dip 70N to 80N to the northeast. The geology is further modified in the northeast corner of Lease C-37210 <br />where coked coal gives evidence of 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 Grand Mesa. <br />The sedimentary strata exposed in the Somerset Coal Field dip at 3N to 5N to the north and northeast, and <br />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 and coals <br />overlain by the Ohio Creek conglomerate and underlain by the Mancos Shale (Figure 2). The Mesaverde <br />Formation is composed of four members, which are, in order of decreasing age, the Rollins Sandstone, the <br />Lower and Upper.Coal members and the Barren member. <br />Minor faulting of limited vertical displacement has been observed in other nearby mines. However, in the <br />Bowie No. 1 Mine, a fault with a displacement of fifty (50) feet was encountered during mining, and <br />drill-liole data indicates the presence of other faults in the life-of-mine area with similar displacements. <br />The faults which have been encountered in these mines tend to be high-angle, normal faults. <br />The steep slopes of the stream valleys and the instability of the rock strata in the North Fork drainage basin <br />have contributed to numerous landslides, mud flows and rock falls. These mass wasting features have <br />been mapped by W.R. Junge of the Colorado Geological Survey and published as an open file report <br />entitled "Geologic Hazards, North Fork Gunnison River Valley, Delta and Gunnison Counties, Colorado." <br />Geologic units exposed in the North Fork Drainage Basin consist of Late Cretaceous to Early Tertiary Age <br />sedimentary strata, Tertiary Age igneous intrusives, and Quaternary Age alluvial and colluvial deposits. <br />The units of the Late Cretaceous in the general area are described below in ascending order. A <br />stratigraphic column representing the geology of the coal member of the Mesaverde Formation in the <br />permit area can be found on Map 2-10, Volume 2, and is found in this document as Figure 3. <br />The Mancos Shale is the oldest formation exposed in the region. This unit is composed of over 4,000 feet <br />of gray marine shales and minor interbedded buff sandstones. This unit is highly erodible and unstable. <br />Erosion and over- steepening of slopes in this formation produce the numerous rock falls and landslides <br />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 is the <br />coal-bearing formation in the region and is divided into four main members - the Rollins Sandstone, the <br />Lower Coal Bearing (Bowie) member, the Upper Coal Bearing (Paonia) member, and the Barren <br />(Undifferentiated) member. <br />12