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Many faults and folds modify the regional synclinal structure. The most significant local fold is the Sage Creek Anticline, located just east of the proposed mine. The Seneca II-W Mine lies on the western flank of this anticline. The largest local structure is the Tow Creek Anticline, located about 10 miles northeast of the permit area. In the permit area, no significant faults or folds have been identified. The local stratigraphic sequence, in ascending order, is the Mancos shale; the Mesaverde Group, which is sub-divided into the Iles and Williams Fork Formations; the Lewis Shale; and the Lance Formation. All are Upper Cretaceous in age. Overlying the Lance Formation are the Tertiary Fort Union and Wasatch Formations. Alluvial deposits are locally present in stream valleys, particularly along the larger streams. Colluvial slides and slumps are also present in canyons and gullies throughout the area. The unit of particular interest to the Seneca II-W Mine is the Upper Cretaceous Mesaverde Group. The Seneca II-W Mine will extract two coal seams from this unit. The Mesaverde, in this part of northwestern Colorado, is divided into two formations: 1) the 1550 foot thick Iles Formation, and 2) the overlying 1100 to 2000 foot thick Williams Fork Formation. The Iles Formation is divided into three members. The basal Tow Creek Sandstone is a massive, fine grained, well sorted sand. The Tow Creek varies from 35 to 125 feet thick. Overlying the Tow Creek is 1200 feet of interbedded shales, sandstones, and coals. The coals, while mined in the vicinity, are too deep to be considered economically recoverable at Seneca II-W Mine. The massive, fine grained, 100 feet thick Trout Creek Sandstone is the uppermost unit of the Iles Formation. Conformably overlying the Iles is the Williams Fork Formation. The lower unit of the Williams Fork Formation is a series of interbedded shales, sandstones, sandy shales and coal. The middle coal group contains the seams of economic importance. Lowermost is the Wolf Creek Coal, which is split into an upper and lower unit. The lower seam is about 16 feet thick, while the upper is about 7.5 feet thick. This coal lies too deep within the proposed permit area to be mined by surface methods. 100 feet above the Wolf Creek Coal is the Wadge Coal. The two seams are separated by interbedded sandstones, shales, siltstones and thin coals. The Wadge Coal Seam is about north-south, and upper and lower seams. from the 10 foot thick sandstones. The princ the most continuous in the area. The outcrop strikes dips 8 to 14 degrees. The Wadge is also split into The lower is two to three feet thick, and is separated upper seam by two to five feet of shales and iple seam to be mined is the Wadge Coal Seam. -14-