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4.0 GEOLOGIC CONDITIONS AND SUBSIDENCE CHARACTERISTICS <br />4.1 Geology <br />The Somerset Coal Field is located on the southeastern margin of the Piceance Basin, <br />which lies north of the Gunnison Uplift, west of the Elk Mountains, east of the <br />Uncompahgre Uplift, and south of the White River Uplift. There are six primary coal <br />seams within the Somerset Coal Field, ranging from 10 ft thick on a single bench of coal <br />to over 20 ft where one or more seams merge (Maleki and others 1997). An estimated <br />1.5 billion tons of bituminous coal lie within the Somerset field. Coal seams B, C, D, E, <br />and F have been mined historically in this basin. The coal seams contain a very well <br />developed cleat set oriented at N58° to 75° E (Carro112003). <br />The regional structural dip of the Mesa Verde Formation is 3° to 5° to the north- <br />northeast. The predominant jointing of sedimentary rocks is N 68° E to N 74° E in the <br />. basin, with secondary jointing at N 18° W (Carroll 2003) to N 35° W. Regional joint <br />patterns have been mapped by Tifft (1995) and Carrol (2003). <br />During extraction of the D 1 to D9 panels, BRL geologic staff studied faulting near <br />the study area using both surface and underground observations. Only one known fault <br />has surface expression in the Hubbard Creek drainage area. This fault was observable <br />along the west side of the drainage only after the DS panel had been extracted directly <br />beneath the outcrop exposure (Hunt 2005). At the Bowie No. 2 Mine to the west, both <br />normal and strike-slip faults have been encountered. The southern portion of the D6 panel <br />is traversed by a N 80-90° Eleft-lateral, strike-slip fault system. The system is a complex <br />array of anastamosing fault planes of variable offsets. Relative motion is 10° to 15° from <br />the horizontal with 5 to 10 ft of total throw down to the south. North of the strike-slip <br />fault, the D6-D9 panels are intersected by some N 60° E normal faults having little to no <br />offsets. It appears that these faults formed as a result of differential movement along the <br />strike-slip fault. This assertion is based on observations showing that throw decreases <br />with increasing distance from the fault to the north, but no such features are found to the <br />Maleki Technologies, Inc. Page 14 <br />