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and sub-bituminous. Although the Twenty Mile Sandstone Member is <br />a regional aquifer noted within the Williams Fork Formation in the <br />Craig, Hayden and Steamboat Springs area, a facies change within <br />the Williams Fork Formation has eliminated the Twenty Mile <br />Sandstone in the Danforth Hills Area. <br />Structure <br />The area around the mine is dominated by the Axial Basin Uplift, an <br />anticline, or arch, which is a southeastward extension of the <br />larger Uinta Mountain Arch. The Axial Basin anticline is an <br />asymmetrical fold, the axis of which trends north 60° west, with <br />strata dipping (inclining) steeper on the south side of the axis <br />than on the north. The south flank of the anticline has several <br />secondary folds trending subparallel and at approximate right <br />angles to the main anticlinal axis. In general, the rocks of the <br />broad anticline have not been stressed sufficiently to cause them <br />to break severely, but a few discontinuous normal faults trending <br />primarily parallel to the anticlinal axis are found in the area. <br />The structure of the permit area is geologically simple. The axis <br />of the Collom syncline, a downward fold, passes through the permit <br />area as shown on the Geology Map (Map 7). Bedding orientation, as <br />measured on surface outcrops, generally has a strike of N 70° W and <br />is characterized by dips from nearly horizontal to as much as 20° <br />to the north. As the mine advances southward, the structure is <br />influenced by the Elkhorn Syncline and a change in attitude of the <br />structure occurs resulting in an eastward dip and nearly north- <br />south strike. Local deviations in this general trend are the <br />result of discontinuous minor folds resulting from differential <br />compaction. <br />During geologic mapping, there was no evidence of faulting in the <br />rock units within the mining area; however, some linear features <br />that may be fault controlled were observed on aerial photographs of <br />the property. Such lineations may also be related to joints <br />(fractures without appreciable movement) in the rock. Three major <br />joint trends that generally coincide with these lineations were <br />observed within the permit area. These are nearly vertical or <br />vertical and strike approximately north 70° west, north 45° west, <br />and north 30° east. In surface exposures, sandstone exhibits <br /> <br />2.04.6-5 <br />