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Fall 2009 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• of the previously observed cracks has been mostly obscured due to re-grading. A significant <br />aspect of Location 4 is the active rockfall/landslide area that has developed on the west side of <br />West Flatiron immediately west of the reclaimed MDW pad over mined Longwall Panel 21. <br />Additional details about this area are discussed later in this section. <br />The previously observed cracks on the reclaimed MDW pad were observed to project to the east <br />side of West Flatiron where a small rockfall and fracture zone is exposed in the sandstone <br />outcrop just beneath the rim (Location 5 of this report). While not as active as the <br />rockfall/landslide on the west side of West Flatiron, this area shows signs of continuous activity <br />as discussed later in this section. <br />Approximately 1,500 feet north of Location 4 is the site of another rockfall/landslide area on the <br />west side of West Flatiron (Location 6). This area is much smaller in size and difficult to <br />observe from along Traverse E-E'. For this reason, Location 6 is discussed under Traverse F-F' <br />from which it is most readily visible. <br />• Also located along Traverse E-E' is Photographic Observation Point 1, an annually visited <br />location used to obtain distant photographs of the 2007 rockfall area above Longwall Panel 21 <br />(Location 4 of this report) for comparative purposes. <br />5.5.1 Location 4 <br />This is the site of five extensive crack zones that were first observed during the spring 2007 field <br />visit. These cracks, observed both in the main West Flatiron drill road and in the drill pad for <br />MDWs 21-32, 21-36, and 21-38, occur above mined Longwall Panel 21 (Map 1). The maximum <br />cumulative extension of the previously-observed crack sequences was estimated to be 2%2 to 3 <br />feet at the time of our site visit in June 2008. However, observations made during our last three <br />field visits found there to be virtually no evidence of these cracks due to the re-grading and <br />reclamation of the drill pad. <br />Previously observed and studied cracks at Location 4 were at one of the two narrowest portions <br />. of the West Flatiron ridge where the overburden depth to the B-seam is about 2,150 feet. In June <br />831-032.791 Wright Water Engineers, Inc. Page 28 <br />April 2010