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Subsidence antl Geologic Fleld Observations <br />Apache Rocks and Box Canyon Mining Areas <br />July 12.15, 2004 <br />Location 12: <br />This location afTords a good view of the eastern part of the Box Canyon mining area and [he <br />southwestern part of the West Flatiron Lease. <br />• A high, natural rcxkl'all potential exists in a ~00 to'_50 tiwt zone within ;md below the thick <br />sandstones of the Ohio Crcck Member of the Mcsaverdc Pomtation (Figures 6, 7, 14, and <br />15). Avery high natural rockfall potential exists in landslide and ra;kfall arctic, such as the <br />area on the west side of ~1'Cet Flatiron above mined longwall panel 22 (sec Section 4.4) <br />• Thr rockfall process involves failure along joints near the edge of the cliffs. The rocks then <br />topple, bounce, anJ roll down the steep slopes below. <br />• A rockl'all and landslide arcs is located un the eastern side of West Flatiron at the first narrow <br />pan of the ridge when traversing northwards (Figure 14). This rockfall/landslide area is <br />located above the southeastern part of un-mined longwall panel 21 near the castctn boundary <br />of the Box Canyon mining area (Map I ). <br />The rockfall potential may be increased slightly when the longwall panels below arc mined. <br />flowevcr, this potential is cstimat~d to be only very slight, based on the very slight to <br />negligible mining eR'ects on the cliffs of Wcst Flatiron to the south above longwall panels 14 <br />attd 15, which have already been mined. <br />• Local cracks similar to the cracks observed on the narrow ridges of 1Vest Flatiron (Fibntre K) <br />were observed on the nurrow part of the ridge on this traverse. The emeks arc as much as an <br />inch wide, and trend genernlly parallel to the trend of the ridge. <br />• Two small landslides, which occur near the boundary between the Box Canyon mining nrca <br />and the West Flatiron Lease, primarily arc a combination of rockfalls and debris flows. They <br />arc located I) above the southeastern comer of un-mined longwall panel Z I (Figure 14) and <br />2) above the eastern part of un-mined longwall panel 19 (Figure IS}-both are near the <br />Wnyht Walar Enymeert. Inc. Pays 29 <br />