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The Office of the State Historic Preservation Officer reviewed the material presented by the applicant and concurs. The Bureau of Land Management had several concerns with the study which the applicant addressed. The operation is in compliance with the requirements of this section. IY. Geology - Rules 2.04.5 and 2.04.6 Detailed discussions concerning interburden, overburden and coal geochemistry may be found in Yolume II, Tab 6, Sections 5 and 6 of the permit application. Local and regional structure, stratigraphy and geologic discussions are presented in Yolume II, Tab 6, Sections 1, 2, 3, and Maps 6-1 through 6-7 and cross sections 6-GX-1 through 6-GX-7 of the permit application. The Seneca II-W Mine is situated in the southeastern synclinal portion of the Sand Wash Structural Basin of northwestern Colorado and south central Wyoming. Exposed strata near the mine site vary in age from late Cretaceous to Quaternary. Most units in the area are marine and none marine sediments. However, some Miocene extrusives are locally present (Figure No. 1). Many faults and folds modify the regional synclinal structure. The most significant local fold is the Sage Creek Anticline, located just east of the 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 subdivided 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 a]so 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. -9-