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Fall 2008 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />0 5.0 TRAVERSES AND OBSERVATIONS IN THE BOX CANYON APACHE <br />ROCKS, AND SOD MINING AREAS <br />A detailed discussion of observations associated with traverses A-A' through N-N' is provided <br />below (see Maps 1 and 2). Many of the photographs taken during the October 2008 field visit <br />are included as figures in the text of this report. Where these images have notable differences <br />from comparable photographs taken in previous years, the older images are also included as <br />figures for comparison purposes. In cases where little or no significant change occurred from <br />previous observation and photographs, only the latest photograph is included. <br />5.1 Traverse A-A' <br />Traverse A-A' begins at a fork in the main Sylvester Gulch road and follows the road up the <br />valley bottom above currently mined Longwall Panel 25 a distance of approximately 3,000 feet <br />to near the mouth of the first east side canyon of Sylvester Gulch. This is the same traverse as in <br />the spring 2008 field visit except that it excludes that portion that departs from the Sylvester <br />Gulch road and winds its way over mined Longwall Panels 19 to 21 to Photographic Observation <br />Point 8. This portion of the traverse was excluded because a new active rockfall/landslide had <br />cut across the road at Location 1 (Map 1). As a result, Traverse A-A' was shortened from the <br />traverse with the same name from the spring 2008 field visit. <br />This shortened traverse has locally deep soil, colluvium, and alluvium ranging in size from clay <br />to boulder as derived primarily from the Barren Member of the Mesaverde Formation. This <br />traverse also includes local bedrock outcrops of the Barren Member as observed as the source <br />area for the rockfall/landslide at Location 1. The overburden depth to the B-seam along this <br />traverse ranges from about 350 to 450 feet. <br />No cracks were observed in the Sylvester Gulch road along this traverse. <br />A relatively small rockfall was noted during the spring 2008 site visit above the drill road where <br />it is located over Longwall Panel 25 (unmined at that time). Because this site was not observable <br />from other locations, this rockfall was difficult to evaluate further during that spring of 2008 <br />831-032.790 Wright Water Engineers, Inc. Page 17 <br />December 2008