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Spring 2009 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />The most recently observed cracks at this location (June 2008), which greatly increased in size <br />and number when longwall mining occurred beneath the area, were individually as much as 12 <br />inches wide and generally trended N30 -40 0 E in an en echelon, or stair - stepping, pattern <br />northward from west to east. The depth of some of these cracks, prior to sloughing, was thought <br />to be as deep as the massive sandstone cliff, which is estimated to be about 50 feet. Previous <br />observations of the two westernmost cracks showed an offset downward to the west along <br />fractures in the massive sandstone of the Ohio Creek Member of the Mesaverde Formation that <br />underlies the now reclaimed drill pad. <br />As noted above, surface expression of the five previously -noted cracks are no longer visible in <br />the MDW pad. However, observations in the native vegetation south of the MDW pad reveal <br />that the crack extensions into that area are still present. Figure 16 is a view of the westernmost <br />crack looking south as it extends southward from the pad. There is a noted musty odor <br />associated with air escaping from portions of this crack. The location of this crack is <br />approximately 15 -25 feet east of the cliff face. There is evidence that the area to the west of this <br />crack which is as much as two feet wide and is unstable and likely to become the next head scarp <br />as additional slabbing and headward erosion occurs. <br />• <br />831 - 032.791 <br />November 2009 <br />Wright Water Engineers, Inc. <br />Page 29 <br />