_GENERAL DOCUMENTS - C1981017 (262)

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-26- spring and early summer are stored in reservoirs. Runoff during late summer through winter is sustained in perennial streams by the release of stored water from small reservoirs and by discharges from ground water aquifers. Geology The three mines within the general area are all located alona the Grand Hogback Monocline. The Grand Hogback forms the steeply dipping eastern edge of the Piceance Basin. The Pennsylvanian through Tertiary aged sedimentary strata which form the Grand Hogback dip lb to 45 degrees to the west. The dip of the strata decrease southward from 40 to 45 degrees at the Sunlight aIine, to 25 to 34 degrees at North Thompson Creek Mines, to 15 to 20 degrees at the Coal Basin mines. It Several smaller structural folds have developed along the Grand Hogback �� LAI Monocline as a result of the igneous activity and the tectonic uplift in the region. The Coal Basin Mines are mining the nose of a plunging anticline, the Coal Basin Anticline. This anticline is thought to be �} 0 related to an igneous laccolith intrusion beneath the southern end of the Grand Hogback t•lonocline. The Hunter' s Point Syncline roughly parallels ��C the Coal Hasin Anticline to the north. Both of these structures trend about N45OW and plunges to the northwest. North of these geologic structures, there are the Wolf Creek Anticline and an unnamed Syncline. These structures roughly parallel the strike of the Grand Hogback Monocline. The Wolf Creek Anticline plunges to the north-northwest. The plunge of the unnamed syncline has not been determined. Most faults along the Grand Hogoack are perpendicular to the strike of the strata and trend east to west. These are high angle normal faults. Along the Grand Hogback, the amounts of vertical displacement and the amount of faulting increases, from 10' s of feet and few faults in the north to 100' s of feet and many faults in the south. A fault in Sections 21 , 22, 23 and 24 of T9S, R89W separates the Hunter' s Point Syncline from the unnamed syncline. This fault separates the area around the Coal Basin Mines and the areas around the other mines into two separate ground water oasins. Sedimentary rock units along the Grand Hogback range in age from the Pennsylvanian Mtge, Eagle Valley Formation to the Tertiary Age, 'Aasatch Formation. The Eagle `!alley Formation is composed of siltstones, shales and evaporite deposits. Due co this unit' s low resistance to erosion, the Crystal and Roaring Fork Rivers have established stream valleys along the strike of this formation. The :Maroon Formation conformably overlies the Eagle Valley Formation. This formation consists Of over 2,000 feet of red to tan arkosic sandstones, siltstone, conglomerates and locally some limestones. Ine l00 tO 2�3,0 foot thick Entrada Formacion unconformaoly overlies :he 'Maroon Formation. This formation is a red to tan sandstone, wnich forms sioces along :ne Grand roaback.