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2005 Subsidence and Geologic Field Observations Box Canyon, West Flatiron, Apache Racks, and South of Divide Mining Areas Overburden Depth Range The overburden depth to the E-Seam is less than it is in many areas of the Box Canyon, West Flatiron, and Apache Rocks mining areas. This is because 1) the topography in the South of Divide mining azea is not as rugged as it is in many parts of these areas, and 2) the E-Seam is 200 to 250 feet stratigraphically higher than the B-Seam. The overburden depth above longwal] panels El through E4 ranges from about 400 to 1,425 feet, panel ES through E8 from 500 to 1,250 feet, panel E9 from 500 to 550 feet, and panels E10 through E12 from 325 to 1,100 feet. 5.1 Traverse Q-Q' Traverse Q-Q' is a foot traverse that begins neaz the Dry Fork mad, the base of a shear zone about 100 feet east of the south dam abutment (Figures IS and 17). The traverse ends at a well- traveled trail above a headscarp that marks the boundary between the lower, more active part of the slide and the upper, less active part of the slide. The overburden depth to the E-Seam ranges from 125 to 375 feet. ' The traverse continues east of the shear zone through humpy, boulder-strewn, brush-covered landslide deposits from point Q to ayoung-looking slump and scarp area underlain by clay and ' silt slide material that contains tension cracks as much as 1 to 1.5 feet wide. It then goes to an upper, older-looking slump and scarp azea (where the shear zone ends) and finally to a well- traveled trail above the more active part of the landslide. The remains of lazge pipe and pipe fittings were observed near the lower end of this traverse. They are very likely the remnants of a drainage system, or systems, which were installed in past years to dewater the active part of the landslide and, thus reduce the pore water pressure and stress on the dam. 931-032.710 Wdght Water Engineers, Inc. Page 36 November 2005