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2006 Subsidence and Geologic Field Observations <br />Box Canyon, West Flatiron, Apache Rocks, and South of Divide Mining Areas <br />' to six years in soft, friable sandstone, and 3) to many decades in hard, durable sandstone <br />t (such as at Apache Rocks). <br />4. Based on field observations and a stereoscopic review of aerial photographs, the area that <br />' has been excavated for the Deer Creek ventilation shaft and escapeway has at least <br />partially cut the lower part of a landslide slump block. Although the slump appears to <br />' have been stable through periods of high precipitation in the past 43 years (based on <br />comparison of 1963, on 2004 aerial photographs, and on field observations in 2006), <br />' continued stability where lateral support has been removed, may depend primarily on <br />providing adequate dewatering of materials in the slip planes or slip zones of the <br />' landslide within the construction area. <br />' S. The rockfall area, which is located at a cliff/overhang area near the old Bear Coal Mine <br />portal, is classified in the very high rockfall potential category, based on <br />' rockfall/landslide mapping by the author. No access road through the area is advised. In <br />addition, steps are recommended to increase lateral support in the cliff/overhang area in <br />' order to 1) prevent any further rockfalls and 2) prevent any potential fracturing in the <br />massive sandstone southward towards the West Elk Mine load out facilities. <br />831-032.750 Wright Water Engineers, Inc. Page 42 <br />December 2006 <br />