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<br />' • Surface extent of landslide movements. <br /> Depth of landslide. <br />' • Nature of landslide materials. <br /> • Evidence of current instability. <br />' • Nature of lineaments. <br />' Surface Extent of Landslide Movements <br />' Figure 1 is a plan which shows the limiu of landslide movements and landslide deposits on the <br />north slope of Jumbo Mountain, based on surface observations, air photo interpretation, and <br />interpretation of drilling results. <br />' Landslide deposits exceeding 100 feet in thickness were penetrated by borings located through <br />a bench or te.~ce which occupies a zone up to 2,~'J fe`; wide between ttie 6,b20-foot and <br />6,850-foot contours (Figure 1). These landslide deposits are underlain by the lower part of the <br />' 'B' seam suggesting that a bedding plane or parting in this seam formed the base of major slide <br />movements. The 'B' seam outcrop, therefore, represents the downslope limit of landslide <br />deposiu. These deposiu clearly represent the remnant of a large ancient ?~~~slide. hfuch of <br />' the original landslide deposit has been removed and reshaped by erosion and consolidation. This <br />is the reason that the surface of the landslide deposit no longer conforms to a normal landslide <br />' configuration and exhibits no evidence of surface movement. <br />' Because of the age of this landslide and the subsequent geomorphic and erosional history, it is <br />not possible to determine the upslope or southern boundary of movement. Two prominent <br />scarps shown on Figure 1 may represent the back of the original slide. These scarps expose in <br />situ strata and, therefore, indicate that movements did not extend any further upslope. The east <br />and west boundaries are also based partly on observations of in situ outcropping strata. t~verall, <br />the limits of the old landslide shown on Figure 1 should be considered as the outermost <br />boundary within which sliding occurred. <br />' Depth of Landslide <br />Figure 2 shows the locations of cross-sections through the old landslide. Figures 3 through 5 <br />aze north-south cross-sections. Figure 6 shows structure contours on the top of bedrock or base <br />of the slide as interpreted from the boring logs. Figure 7 shows isopachs of the landslide <br />thickness based on the same data. <br />-2- <br />0: \Off\30\JFT\ARCO-Rpt.lkl <br />