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Exhibit 60C <br />Subsidence Evaluation and 2004 Geologic Hazard Field Observations <br />West Flatiron Lease Area <br />9.0 CONCLUSIONS <br />After six yeazs of field observations (1999 to 2004), three years pre-mining and three years post- <br />mining, in Apache Rocks and Box Canyon mining areas, no subsidence cracks have been <br />observed in alluvium above the longwall panels that were mined. In particular, no subsidence <br />features (cracks or bulges) were observed in Deep Creek within the area of mining influence of <br />mined longwall panels 14 through 17, nor were any subsidence features observed in Sylvester <br />Gulch above mined longwall panels 14 through 16. The overburden depth to the B Seam in both <br />stream lengths undermined by the mined longwall panels ranges from about 900 to 1,600 feet. <br />The alluvium along the portions of the streams of Deep Creek and Sylvester Gulch above the <br />mined longwall panels contains a major percentage of silt and clay, which was derived from the <br />Wasatch Formation during erosion and deposition. The reason for the lack of cracking in <br />alluvium is most likely that this fine silt- to clay-sized material and overlying soil yields without <br />• cracking or bulging as it deforms as a discrete unit in the subsidence process. As previously <br />stated (regarding the downwarping process above mined longwall panels), the cracks only occur <br />in the tension zone. This tensile zone becomes compressive at the neutral surface. <br />Based on the observations described above, these same results will also likely apply to the Raven <br />Gulch area. It is unlikely that cracks will occur in the colluvium and alluvium in the stream <br />valley of Raven Gulch and its southwest-trending tributary, adjacent to longwall panels 18 <br />and 19. The overburden thickness above the panel centerlines of these panels ranges from about <br />800 to 900 feet. <br />It is unlikely that the landslides on the east flank of West Flatiron will be affected by mining <br />longwall panels 19 and 21. This conclusion is based on the fact that no changes were observed in <br />the landslides-located on the southwest end of West Flatiron above longwall panels 14 and <br />15-when these panels were mined. <br />• <br />831-032.650 Wright Wator Engineers, Inc. Page 27 <br />November 2004 <br />