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<br /> <br />_17_ <br />Over half of the precipitation occurs as snowfall. The remaining <br />precipitation 15 mostly concentrated in high energy thunderstorm events <br />in late spring and early summer. Some of the runoff flows during the <br />spring and early summer are stored in reservoirs. Runoff during late <br />summer through winter 15 sustained to perennial streams 6y the release of <br />stored water from small reservoirs and by discharges from ground water <br />aquifers. <br />Geology <br />The three mines within the general area are all located along the Grand <br />Hogback Monocline. The Grand Hogback forms the steeply dipping eastern <br />edge of the Ptceance Basin. The Pennsylvanian through Tertiary aged <br />sedimentary strata which form the Grand Hogback dip 75 to 45 degrees to <br />the west. The dip of the strata decrease southward from 40 to 45 degrees <br />at the Sunlight Mine, to 25 to 34 degrees at North Thompson Creek Mines, <br />to 15 to 20 degrees at the Coal Basin Mines. <br />Several smaller structural folds have developed along the Grand Nogback <br />Monocline as a result of the igneous activity and the tectonic uplift 1n <br />the region. The Coal Basin Mines are mining the nose of a plunging <br />anticline, the Coal Basin Anticline. This anticline is thought to be <br />,related to an igneous laccolith intrusion beneath the southern end of the <br />Grand Hogback Monocline. The Hunter's Point Syncline roughly parallels <br />the Coal Basin Anticline to the north. Both of these structures trend <br />about N45oW and plunges to the northwest. North of these geologic <br />structures, there are the Wolf Creek Anticline and an unnamed Syncline. <br />These structures roughly parallel the strike of the Grand Hogback <br />Monocline. The Wolf Creek Anticline plunges to the north-northwest. <br />The plunge of the unnamed syncline has not been determined. <br />Most faults along the Grand Hogback are perpendicular to the strike of <br />the strata and trend east to west. These are high angle normal faults. <br />Along the Grand Hogback, the amounts of vertical displacement and the <br />amount of faulting increases, from 10'5 of feet and few faults in the <br />north to 100'5 of feet and many faults in the south. A fault fn Sections <br />21, 22, 23 and 24 of T9S, R89W separates the Hunter's Point Syncline from <br />the unnamed syncline. This fault separates the area around the Coal <br />Basin Mines and the areas around the other mines into two separate ground <br />water basins. <br />Sedimentary rock units along <br />Pennsylvanian Age, Eagle Val <br />Formation. The Eagle Valley <br />and evaporate deposits. Due <br />the Crystal and Roaring Fork <br />the strike of this formation <br />the Grand Hogback range in age from the <br />ley Formation to the Tertiary Age, Wasatch <br />Formation is composed of siltstones, shales <br />to this unit's low resistance to erosion, <br />Rivers Have established stream valleys along <br />