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<br />' ~ December 1986 <br />4.2 Geology <br />863-2052 <br />The Wadge and Wolf Creek seams lie within the Williams Fork For- <br />mation of the Mesaverde Group. The Wadge seam, which varies from <br />7 to 11.5 feet in thickness, overlies the Wolf Creek seam by <br />approximately 180 feet. The Wolf Creek ranges in thickness from <br />11 to 21 feet. The strata within the Little Middle Creek tract <br />strike approximately east-west and dip at an average of 10 de- <br />grees to the north. <br />Geotechnical data are available for the Mesaverde strata in the <br />vicinity of Area 51, which is located east of the Little Middle <br />Creek tract. Historic mine data resulting from geotechical <br />drilling, mapping, and laboratory testing indicate that the <br />sandstone/shale sequence which overlies the Wadge seam is rela- <br />tively uniform, generally competent, and of moderate strength. <br />The Wadge overburden has resulted in stable highwalls and pro- <br />duces a spoil with good strength characteristics. Even the black <br />shales ("underclays" or "fireclays") which directly overlie and <br />underlie the Wadge were found to be of low to medium strength. <br />These shales, which are widely recognized as a principal source <br />of highwall and spoil instability in many surface coal mines, <br />have never been associated with any instability in Area 51. <br />The overburden below the Wadge generally consists of an alter- <br />nating sequence of sandstones, shales, claystones, and silt- <br />stones. Drill logs indicate that there is an increased shale <br />content below the Wadge. An evaluation of the distribution of <br />overburden materials above the Wadge and Wolf Creek seams by CYCC <br />(1986) is given in Table 3. <br />Golder Associates <br />