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Fall 2009 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• previous visit. This area is described in more detail in Section 5.1.1 as Location 1 of Traverse A- <br />A' (Map 1). <br />Another active rockfall/landslide area visited was that observed on the west and east sides of <br />West Flatiron during the spring 2007 and fall 2008 field visits, respectively. Location 4 (Map 1) <br />is located in the headwater region of Box Canyon and in one of the most narrow parts of West <br />Flatiron ridge at a site where cracks (most likely gravity-induced) were first observed. Active <br />cracking and slabbing above mined Longwall Panel 21 both on the west and east sides of West <br />Flatiron appears to have lessened. The rockfall area on the east side of West Flatiron is identified <br />as Location 5 (Map 1). Cumulative extension of the surface cracks, as observed in June 2008, <br />was on the order of 2.5 to 3 feet. As of October 2, 2008, the area historically used to monitor <br />these surface cracks (a MDW pad) was reclaimed and nearly all evidence of surface cracks has <br />been obscured except at the sandstone cliff face. Aside from a few remaining MDW pads near <br />the north end of West Flatiron, mining-related activities in this area are complete. Nonetheless, <br />the potential for more cracking and rockfall activity on the west- and east-facing cliff faces over <br />• Longwall Panel 21 is high. Such activity is expected to have an effect only on surface features, <br />particularly vegetation. <br />Approximately 1,500 feet north of the rockfall/landslide area first observed in spring 2007 is a <br />second rockfall area observed for the first time during the June 2008 site visit. This area is <br />described in this report as Location 7 (Map 1) and is located on the west side of another narrow <br />portion of the West Flatiron ridge between mined Longwall Panels 19 and 20. This rockfall area <br />is considerably smaller than its neighbor to the south, as shown on Map 3, and in the head of the <br />Box Canyon drainage. <br />The Box Canyon drainage has no human inhabitants or access roads. Continued <br />rockfall/landslide activities will have limited effect on the Box Canyon drainage or access road <br />but will likely affect the drill road on West Flatiron and the MDWs which remain in operation <br />there. However, access to West Flatiron and the MDW pads is expected to decrease now that <br />mining has been completed on all the B-seam panels in the Box Canyon Mining Area. <br />• <br />831-032.791 Wright Water Engineers, Inc. Page 3 <br />April 2010