2012-01-06_PERMIT FILE - C1982057 (18)

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of the workable coal seams within this group is called the Dry Creek coal bed and is situated about 400 feet above the Twentymile sandstone member. The Lewis shale conformably overlies the Mesaverde Group and, like the upper unit of the Williams Fork Formation, is highly variable in thickness. I[ is principally a homogenous marine shale. It tends to be more sandy in the upper portion of the formation and may contain a few lenticular sandstone layers (Figure 6-21. The youngest Cretaceous rock formation exposed in the area is the Lance Formation. It conformably overlies the Lewis shale end is about 1,000 to 1,500 feet thick. The Lance Formation is comprised of interbedded shale, sandy shale, sandstone, and coal. Some of the sandstone layers can be rather thick labout 100 feetl~ The only coal bed present in the Lance Formation which is of any economic significance is the Kimberly coal bed which has been found to be as thick as 14 feet in some areas (Bass et al., 19551. The Fort Union Formation of Tertiary age lies above the Lance Formation. It consists of interbedded sandstone, shales, and coals deposited during the Paleocene epoch and is approximately 1,400 feet thick (Bass et al., 19551. Compared to the Lance Formation, the sandstones are coarser, the shales are lighter gray in color, and there are more coal layers. The thickest regional coal seam present in the Fort Union Formation is the Seymour Coal. • The Wasatch Formation of Eocene age unconformably overlies the Fort Union Formation. It is comprised primarily of fresh water stream-laid sandstone and shale deposits. Unconsolidated alluvial, terrace, and surficial deposits of Quaternary age overlie the Wasatch Formation in some areas, particularly along larger streams. Site Specific Geology Structure. The Seneca II-W Mine area is situated within the rugged Williams Fork Mountains on the western limb of the Sage Creek Anticline (Figure 6-11. The axis of the Sage Creek Anticline is situated about one-half mile east of the eastern edge of the Seneca II-W permit area and trends northwesterly (Exhibit 6-11. The rock units in the permit area dip about 8 to 14 degrees to the west (Exhibit 6-11 and do not appear to be affected by any significant faulting or folding within the Seneca II-W permit area as can be seen on Exhibits 6-2, 6-3, and 6-GX-1 through 6- GX-9. Exhibits 6-2 end 6-3 are structural contour maps depicting the top of the Wadge coal seam; and Exhibits 6-GX-1 through 6-GX-9 are geologic cross sections. 5 Revised 9/98