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i <br /> f <br /> k � <br /> r. fciy. <br /> _ f <br /> LP �. <br /> Map T Seneca IIW Mine permit boundary and waterbodies. <br /> The Seneca IIW Mine is situated in the southeastern synclinal portion of the Sand Wash Structural <br /> Basin of northwestern Colorado and south central Wyoming. Exposed strata near the mine site vary <br /> in age from Late Cretaceous to Quaternary. Most units in the area are sedimentary. However, some <br /> Miocene extrusives are locally present. Many faults and folds modify the regional synclinal structure; <br /> however, no faults have been identified at the site. The most significant local fold is the Sage Creek <br /> Anticline, located just east of the mine. Rock units dip 8 to 14 degrees to the west. The Seneca <br /> IIW Mine lies on the western flank of this anticline. The largest local structure is the Tow Creek <br /> Anticline, located about 10 miles northeast of the permit area. <br /> The local stratigraphic sequence, in ascending order, comprises the Mancos Shale; the Mesaverde <br /> Group,which is subdivided into the Iles and Williams Fork Formations; and the Lewis Shale. See <br /> the Exhibit 6-GX,the geologic cross section map series in the permit application package for further <br /> detail. The Iles Formation is divided into three members. The basal Tow Creek Sandstone is a <br /> massive, fine-grained, well sorted sand. The Tow Creek varies from 35 to 125 feet thick. <br /> Overlying the Tow Creek are 1200 feet of interbedded shales, sandstones, and coals. The coals, <br /> while mined in the vicinity, are too deep to be considered economically recoverable at the Seneca <br /> IIW Mine. The massive, fine grained, 100 feet thick Trout Creek Sandstone comprises the <br /> uppermost unit of the Iles Formation. <br /> Conformably overlying the Iles is the Williams Fork Formation. The lower unit of the Williams <br /> Fork Formation is a series of interbedded shales, sandstones, sandy shales and coal. The middle <br /> coal group contains the seams of economic importance. Four coal seams of economic importance <br /> are found in the Williams Fork Formation. These seams,in ascending order consist of,the Wolf <br /> Creek, Sage Creek, Wadge and Lennox coals. Due to discontinuous occurrence of the Sage Creek <br /> Page 5 of 37 <br />