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Gunnison River and its tributaries, with several remnant alluvial terraces above the valley of the <br /> North Fork. Proceeding downstream below the town of Somerset, the canyon widens. At the <br /> town of Paonia, the canyon has given way to a broad alluvial plain with interspersed remnant <br /> alluvial terraces. The coal mined is located in the Somerset Coal Field. The strata exposed in <br /> the Somerset Coal Field consist of the Mancos Shale and the coal bearing Mesaverde Formation <br /> of Upper Cretaceous Age, and of the Ohio Creek Conglomerate, the Wasatch Formation and the <br /> Quartz Monzonite Porphyry of Early Tertiary Age. Coal was mined from the Mesaverde <br /> Formation, a 2,500 foot thick sequence of sedimentary strata overlain by the Ohio Creek <br /> Conglomerate and underlain by the Mancos Shale. The strata in the Elk Creek Mine permit area <br /> dip three to five degrees north northeast within the permit area, but varies locally. <br /> The Mesaverde Formation contains a number of coal-bearing members. The Somerset Mine <br /> mined coal from the B 2 seam of the lower coal bearing (Bowie) member of the Mesaverde <br /> Formation. The Sanborn Creek and Sanborn Creek East additions mined the B and C seams of <br /> this member. The Elk Creek Mine ramped down to the D-seam and mined that level. The <br /> Lower Coal member ranges from 260 to 350 feet thick in the Somerset Coal Field and bears <br /> three minable coal seams. This member consists of interbedded and lenticular sandstones, <br /> siltstones and coals, and is overlain by a massive sandstone, 25 to 225 feet thick which lies <br /> directly on the C seam and marks the bottom of the upper coal member. <br /> Three categories of potential aquifers exist in the general area: alluvial deposits associated with <br /> the North Fork of the Gunnison River and its tributaries, the Rollins Sandstone, and lenticular <br /> discontinuous sandstones of the Upper Mesaverde Formation. <br /> The largest alluvial aquifers are associated with the North Fork of the Gunnison River. Smaller, <br /> more isolated alluvial aquifers are associated with several tributaries of the North Fork. <br /> The Rollins Sandstone is the only known sandstone with sufficient porosity and lateral extent to <br /> be considered a regional bedrock aquifer. The only wells in the region which are completed in <br /> this aquifer are located near the Hawk's Nest Mine along the North Fork of the Gunnison. <br /> Localized perched bedrock aquifers exist in the discontinuous, lenticular, fine grained sandstones <br /> of the Upper Mesaverde Formation. The amount of ground water in these sandstones is <br /> controlled by faulting and fracturing of the strata(secondary porosity) and the topography of the <br /> recharge area. No known wells are completed in the sandstones of the Upper Mesaverde <br /> Formation above the mine workings. <br /> The valley in which the towns of Paonia and Somerset are situated is semi-arid, with annual <br /> precipitation averaging about 15 inches per year. Mean annual precipitation increases with <br /> elevation, reaching over 40 inches per year near the summit of Mt. Owen. The May to <br /> September precipitation is five inches for the lowlands and 13 inches for the mountain peaks. <br /> This indicates that snowfall patterns play an important part in determining the hydrologic <br /> conditions of the area. Temperature extremes at Paonia have ranged from—28°F in January to <br /> 100°F during July and August. The average annual temperature is approximately 49°F. <br /> Snowfall averages 58 inches per year. <br /> 6 <br />