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Spdng 2009 Subsidence and Geologic Field Observations <br />SOK Canyon, Apache Rocks, and South of Divide Mining Areas <br />F - I <br />J <br />Figure 35. Eastward telephoto view from spring 2009 of the headscarp area shown in the <br />preceding figures. Note the active rockfall /landslide on West Flatiron can be seen in the left <br />background. <br />5.8.5 Photographic Observation Point 5 <br />• Photographic Observation Point 5, (Map 1) was established in April 2007 to provide a more <br />complete view of the same headscarp area depicted from Photographic Observation Point 4. Due <br />to a locked gate this location was not visited during the spring 2009 field visit. <br />5.9 Location 10 <br />This is the site of subsidence cracks at Apache Rocks (Figures 36 through 40). The cracks, <br />which are straight to branching, as much as 175 feet long, 25 to perhaps 30 feet deep, and as <br />much as 5 inches wide, are located in the tension zone above the southern edge of the gate road <br />pillars between mined Longwall Panels 12 and 13 in the B -seam. The area is therefore in a <br />double extension zone produced by the mining of Panels 12 and 13. <br />The cracks trend primarily N65 -75 °E, but locally diverge to N40 0 E, N80 0 E, and E -W. The <br />overburden depth to the B -seam is about 1,350 feet. More cracks were observed soon after <br />mining than are now present. Some of the smaller cracks in the northernmost part of the initial <br />• crack area have closed, or healed and sealed, a year or two after they formed. There currently are <br />831- 032.791 Wright Water Engineers, Inc. Page 46 <br />November 2009 <br />