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slump to the floor with <br />some coherence, instead <br />of a more chaotic, rapid, <br />and dangerous rockslide <br />that would have crashed <br />down with significant <br />rockfall debris scattered <br />onto the quarry floor where <br />equipment was located. <br />3. From examination of earlier <br />aerial photography. the <br />slope of the west wall of <br />4 <br />i <br /> <br />area MV was loaded 4 <br />spoils from the active <br />excavation of a large bent. - - <br />Figure 3 Steep formational dips in limestone beds of active <br />in weathered granite that quarry in Area H (the hole). Location is directly east from the <br />was part of the special use toe of the rockslide, looking to the north. <br />permit by USFS in 2001. <br />This material was cast onto the slope as a large fan, loading the dipping sedimentary <br />strata on the highest part of the west quarry wall (Area MV). <br />Deviation from the mining plan: The mining of the hole exposed too much of the base of <br />the quarry wall. The mine permit amendment stated that "it is not expected that any <br />more than X of the total length of the west wall of the Hole will be unsupported by <br />backfill (or unmined rock) at any one time. Thus, any large scale instability that might <br />occur would be limited in scope simply because most of the west wall will either be <br />supported by backfill or by native rock yet to be ruined. " That doesn't appear to be the <br />case. Figure 1 illustrates that much of the hole was open and the quarry wall was <br />essentially unsupported prior to the failure. The limited amount of fine-material fill <br />located on the south end to develop the access ramp was not effective in supporting the <br />slope and was displaced laterally about 80 feet by the rockslide. On the north side of <br />Area H, buttressing of the slope by the elevation of the active bench that was being <br />drilled was obviously more effective. A well-defined pressure ridge in the rockslide <br />rubble developed against this bench (Figure 4). <br />7