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<br /> <br />Wasatch Formation and the Quartz Monzonite Porphyry of Early Tertiary Age <br />(Figure 2). Coal is mined from the Mesaverde Formation, a 2,500 foot thick <br />sequence of sedimentary strata overlain by the Ohio Creek Conglomerate and <br />underlain by the Mancos Shale. The strata in the Somerset Permit area dip <br />three to five degrees north-northeast. <br />The Mesaverde Formation contains two coal bearing members. The Somerset Mine <br />mined coal from the B-2 seam of the lower coal bearing (Bowie) member of the <br />Mesaverde Formation. The Sanborn Creek and Sanborn Creek East additions to <br />the mine will extract coat from the B and C seams of this member. The Lower <br />Coal member ranges from Z60 to 350 feet thick in the Somerset Coal Field and <br />bears three minable coal seams. This member consists of interbedded and <br />lenticular sandstones, siltstones and coals, and is overlain by a massive <br />sandstone 25 to 225 feet thick which lies directly on the C seam and marks the <br />bottom of the upper coal member. <br />Three categories of potential aquifers exist in the general area: alluvial <br />deposits associated with the North Fcrk of the Gunnison River and its <br />tributaries, the Rollins Sandstone, and lenticular discontinuous sandstones of <br />the Upper Mesaverde Formation. <br />The largest alluvial aquifers are associated with the North Fork of the <br />Gunnison River. Smaller, more isolated alluvial aquifers are associated with <br />several tributaries of the North Fork. <br />The Rollins Sandstone is the only known sandstone with sufficient porosity and <br />lateral extent to be considered a regional bedrock aquifer. The only wells in <br />the region which are completed in this aquifer are located near the Hawk's <br />Nest Mine along the North Fork. <br />Localized perched bedrock aquifers exist in the discontinuous, lenticular, <br />fine-grained sandstones of 'the Upper Mesaverde Formation. The amount of <br />ground water in these sandstones is con*.rolled by faulting and fracturing of <br />the strata (secondary porosity) and the topography of the recharge area. No <br />known wells are completed in the sandstones of the Upper Mesaverde Formation <br />above the mine workings. <br />The valley in which the towns of Paonia and Somerset are situated is semi- <br />arid, with annual precipitation averaging about 15 inches per year. Mean <br />annual precipitation increases with elevation, reaching over 40 inches per <br />year near the summit of Mt. Owen. The May-September precipitation is five <br />inches for the lowlands and 13 inches for the mountain peaks. this indicates <br />that snowfall patterns play an important part in determining the hydrologic <br />conditions of the area. Temperature extremes at Paonia have ranged from -26°F <br />in January to 100°F during July and August. The aaerage annual temperature i5 <br />approximately 49°F. Snowfall averages 56 inches per year. <br />The general area in which the Somerset Mine is located is characterized by <br />steeply sloping mountains covered either ~~,ith tall shrub vegetation, <br />particularly cakbrush and serviceberry, or ;tends of cincn and juniper trees. <br />Drainages in the area are lined with riparian vegetation communities a'•ong the <br />stream banks. Some of the more love' areas have been cleared and suopo•.t <br />limited livestock grazing; haNever, for the most part, the surrounding land is <br />-5- <br />