2008-09-29_PERMIT FILE - C1981019A (28)

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RULE 2 PERMITS The Williams Fork Formation is the predominant coal-bearing formation in the Mesa Verde Group. Mesa Verde coals associated with the Fairfield Group, the coal-bearing zone above the Trout Creek Sandstone, rank in quality about midway between bituminous and sub-bituminous. Although the Twenty Mile Sandstone Member is a regional aquifer noted within the Williams Fork Formation in the Craig, Hayden and Steamboat Springs area, a facies change within the Williams Fork Formation has eliminated the Twenty Mile Sandstone in the Danforth Hills Area. Structure The area around the mine is dominated by the Axial Basin Uplift, an anticline, or arch, which is a southeastward extension of the larger Uinta Mountain Arch. The Axial Basin anticline is an asymmetrical fold, the axis of which trends north 60° west, with strata dipping (inclining) steeper on the south side of the axis than on the north. The south flank of the anticline has several secondary folds trending subparallel and at approximate right angles to the main anticlinal axis. In general, the rocks of the broad anticline have not been stressed sufficiently to cause them to break severely, but a few discontinuous normal faults trending primarily parallel to the anticlinal axis are found in the area. The structure of the permit area is geologically simple. The axis of the Collom syncline, a downward fold, passes through the permit area as shown on the Geology Map (Map 7). Bedding orientation, as measured on surface outcrops, generally has a strike of N 70° W and is characterized by dips from nearly horizontal to as much as 20* to the north. As the mine advances southward, the structure is influenced by the Elkhorn Syncline and a change in attitude of the structure occurs resulting in an eastward dip and nearly north-- south strike. Local deviations in this general trend are the result of discontinuous minor folds resulting from differential compaction. During geologic mapping, there was no evidence of faulting in the rock units within the mining area; however, some linear features that may be fault controlled were observed on aerial photographs of the property. Such lineations may also be related to joints (fractures without appreciable movement) in the rock. Three major joint trends that generally coincide with these lineations were observed within the permit area. These are nearly vertical or vertical and strike approximately north 70° west, north 45° west, and north 30° east. In surface exposures, sandstone exhibits joints more readily than highly oxidized and weathered coal beds do; however, both have undergone similar stresses and have developed similar readjustment features that are apparent in the subsurface. The site specific stratigraphy is described in Exhibit 6, Geological Information, and is graphically shown on the Geologic Cross Section A-A' (Map 8) and the Geologic Cross Section B-B' (Map 9). Three additional geologic cross sections (C-C', D-D', and E-E') that show the coal seam geometry and pit limits are provided in Map 9A. The topographic locations of the geological cross sections are found on the Geology Map (Map 7). The coal seams to be mined at the Colowyo operation are the "Y3",46Y26,64X6,44A264,66A346,4B 146, "C", "D", "E", and "F" coal seams. These coal seams are found in the Williams Fork Formation and lie within a sequence of sedimentary rocks characterized by sandstones, claystones, siltstones, shales and carbonous and silty shales. This sedimentary sequence is typical of cyclothems deposited along the linear clastic shoreline located at the western edge of an epicontinental seaway which was located in interior western North America during most of Late Cretaceous time. The analyses of the various coal seams to be mined are shown in Table 2.04.6-1, Typical Coal Seam Analyses. Rule 2 Permits 2.04.6-2 Revision Date: 6/23/08 Revision No.: MR-91