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Fall 2007 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />5.4 Traverse D-D' <br />Traverse D-D' is a short traverse that starts at the fork in the main West Flatiron drill road (C-C' <br />traverse) and heads to the drill pad containing MDWs 19-04 and 19-05. This traverse is above <br />the eastern part of mined longwall panel 19 primarily in clays and silts of the Wasatch <br />Formation. Overburden depth to the B-seam is 2,200 to 2,250 feet. <br />Point D', which also is photographic observation point 2, provides a good southward view of the <br />rockfall/landslide area above mined longwall panel 22. This is an annual observation location <br />for this area because this vantage point provides a good view of the steep cliffs along the west <br />side of West Flatiron. <br />5.4.1 Photographic Observation Point 2 <br />Photographic observation point 2 was used in the past two years to observe and photograph a <br />rockfall/landslide area (location 6) located 4,400 feet south of the observation location in the <br />upper, massive sandstone cliff of the Ohio Creek Member of the Mesaverde Formation (Figure <br />18). <br />5.4.2 Location 6 <br />Location 6 is a rockfall/landslide area located above the rigid chain pillars (three-pillar entry <br />system) that separate panel blocks 18, 19, 20 and 21 (to the north) from panel blocks 22, 23, and <br />24 (to the south). The rockfall/landslide is therefore located in an area of maximum tensile <br />strain, both due to mine geometry and topography. It is also in an area of high to very high <br />natural rockfall potential (Map 3). Figures, D-4, and D-5 show the same area as observed in <br />2006 and 2005, respectively. <br />With the exception of being more weathered in appearance, the rockfall/landslide area has not <br />changed appreciably since July 2005, even though a change was discussed incorrectly in the <br />video footage taken of the area in 2006. The rockfall/landslide area located above and east of the <br />main rockfall/landslide appears to be more evident in the 2005 image because it was taken from a <br /> <br />831-032.780 Wright Water Engineers, Inc. Page 30 <br />November 2007 <br />