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2005 Subsidence and Geologic Field Observations <br />Box Canyon, West Flatiron, Apache Rocks, <br />and South of Divide Mining Areas <br />Desiccation cracks can often be recognized by their irregulaz, branching, and diverging pattern- <br />less regular than typical subsidence cracks. Some of the lazgest desiccation cracks in the West <br />Elk mine area were observed in clays of the Barren Member of the Mesaverde Formation in the <br />Horse Gulch-Minnesota Reservoir area where there had been no mining. The larger, more <br />regulaz desiccation cracks and construction cracks may be confused with subsidence cracks in <br />areas where mining has occurred. However, transverse and longitudinal tension cracks caused by <br />subsidence have a definite spatial relationship to the geometry of the longwall mining panel <br />causing the cracks. <br />2.4 Gravity-Induced Tension Cracks <br />Cracks have been observed on high, steep ridges and near cliffs, and in landslides, in the Box <br />Canyon, West Flatiron, Apache Rocks, and South of Divide mining areas. The cracks look very <br />much like subsidence cracks, but they cannot be, because no mining had been done in the area <br />where they were observed. The extensive crack on a narrow ridge on West Flatiron, which was <br />as much as 3.5 in wide and 150 feet long in August 2002, is a good example of agravity-induced <br />' crack (Dunrud 2002). It was easy to determine that this was not amining-related crack because <br />no mining had occurred in the area. The possibility of gravity-induced cracking in the rugged <br />' country above planned mining activities at the West Elk mine is a good reason to perform <br />baseline studies of the area prior to mining so that these features can be documented. <br />831-032.710 Wright Water Engineers, Inc. Page 6 <br />November 2005 <br />