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Memorandum to Christine Johnston <br />October 7, 1999 <br />Page 12 <br />• Open cracks, which trend northward <br />generally parallel to outcrop and range <br />from a few inches to as much as 2 ft wide, <br />occur near cliff edge. No recent cracking <br />was observed; the bottoms of the cracks <br />contain undisturbed soil, vegetation. and <br />plant debris (Figure 7). <br />• These pre-mining features are the result of <br />natural mass-gravity movement (gravity <br />spreading, spalling) in jointed bedrock due <br />to lack of lateral support. <br />Location 14. Located in claystones of the Wasatch Formation on the northward point on West <br />Flatiron above the eastern part of projected longwall Panel l8. <br />• Overburden depth to B-Seam is about 2,150 ft. <br />• Cracks, a few inches to perhaps l ft wide, <br />are locally present along cliff edge. <br />Cracks trend mostly northward <br />subpazallel to ridge, but also trend <br />perpendicular to this direction locally <br />(Figure 8). <br />• Cracks also locally occur in colluvium and <br />soil in the firs[ narrows south of point. <br />Cracks are likely caused primarily [o <br />mass-gravity spreading of underlying <br />Ohio Creek Sandstone,' but the <br />desiccation process may also be a <br />contributing factor. <br />Wright Water Engincers, Inc., 2490 W. 26'" Avenue, Ste. 100A, Derner, CO 80211 <br />Tel. 303/480.1700; Fax. 303/480.1020, e-mail:knivright@wrightwater.wm <br />