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Wasatch Formation and the Quartz Monzonii:e 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 strai:a 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 ecnd Sanborn Creek East additions to <br />the mine will extract coal from the B anti C seams of this member. The Lower <br />Coal member ranges from 260 to 350 feet i:hick 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 Fork 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 controlled 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 -28°F <br />in January to 100°F during July and August. The average annual temperature is <br />approximately 49°F. Snowfall averages 53 inches per year. <br />The general area in which the Somerset Mine is located is characterized by <br />steeply sloping mountains covered either with tall shrub vegetation, <br />particularly oakbrush and service berry, or stands of pinon and juniper trees. <br />Drainages in the area are lined with riparian vegetation communities along the <br />stream banks. Some of the more level arias have been cleared and support <br />limited livestock grazing; however, for the most part, the surrounding land is <br />C~ <br />-5-- <br />