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2004 Geologic Hazard Field Observations <br />South of Divide Mining Area <br />longwall panel 17) and in the upper parts of Sylvester Gulch (above mined longwall panels 14- <br />16). <br /> <br />• <br />The probable reason for the lack of cracking in alluvium is that the fine silt- to clay-sized <br />material and overlying soil can yield without cracking or bulging as it deforms as a discrete unit <br />in the subsidence process. The estimated thickness of the alluvium observed during geologic <br />mapping activities ranges from about 25 feet to as much as 150 feet in the West Elk mining <br />area-including the South of Divide mining azea. <br />Based on annual field subsidence observations in the Apache Rocks and Box Canyon mining <br />areas, the maximum crack depth in bedrock outcrops and weathered bedrock areas in the South <br />of Divide mining azea is estimated to be: 1) 5 to 15 feet in terrain sloping less than, or equal to, <br />30 percent, and 2) 10 to 35 feet in the same terrain sloping more than 30 percent (Table 1). <br />831-032.621 Wright Water Engineers, Inc. Page 17 <br />November 2004 <br />