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2005 Subsidence and Geotogrc Field Obsorvationa <br />Box Canyon, Wosl Flatiron, Apache Flocks, <br />and South of Divide Mining Areaa <br />4.2 Highway 133 Landslides <br />4.2.1 Location 3 <br />locution 3 is on the north side of, and ?W to 300 fc;et above, the North Fork. The Icx.ation <br />affords a good southern view of the landslides, which occurred after Highway 133 was <br />constructed in the early 1980s. Most of the landslides occurred during periods of high <br />precipitation during the mid 1980s and the mid 1990s after lower parts of old landslides and <br />colluvium were removed during construction of the road cut for the realignment of Highway 133. <br />The GPS la;ation of laxatiun 3 is'_89,d38m L'•,-3,31 1.787m ~1 (circle of error 3-htn). <br />Landslide East of the Mouth of Box Canyon. <br />The Landslide ease of the mouth of Box Canyon cxcuned suddenly in the mid 19d0s as a <br />detached block (Figure 3). This dynamic even[ caused a noise and tremor that was heard and felt <br />at the Wcst Elk mine ofticc 8,000 to 9,OW (eet west of the event. <br />1'hc overburden depth to the B•Scam rtnges from about -3W feet in the toe arcs south of State <br />Highway 133 to about 900 feet at the top of the head scarp. The head scarp area, in addition to <br />the upper parts of this landslide, arc projuacd to lx within the area of mining influence of the <br />tailgalc entries of northeastern part of un-mined longwall panel 18. <br />The slide, which horizontally and vertically displaced the highway, occurred more than ten years <br />after highway construction was completed. 7•he landslide involves bedrock that initially appears <br />to have split off the main outcrop and moved essentially vertically downward. The landslide now <br />consis[s (from south to north) of 1) a steep to vcntcul head scarp SO to lW feet high, 2) an <br />elongate depression, 3) a main slump block that still contains vertically oriented pint trees, and <br />d) a lower run-oul zone that contains la:al additional slumping and debris flows that mach the <br />southern bunk of the North Fork IFigurcs 3 and 4). <br />831.032.710 Wnght Water Engineers, Inc, Pege 11 <br />November 2005 <br />