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Evaluation of Bear No. 3 Mine Landslide <br />events show dramatically as steep, baze, linear streaks on aerial photos or field observations. <br />Several can be seen both east and west of the November 1997 slide (Figure 2). <br />Potentially unstable slopes have been mapped over much of the area. In an environment such as <br />this, any steep colluvial slope has the potential to become unstable. Because of the highly <br />varying slopes and varying physical properties of the material a detailed or exact prediction of <br />their behavior is difficult to impossible. Interestingly, the November 1997 slide azea was not <br />mapped as a potentially unstable slope on any of the maps, but Rocky Mountain Geotechnical <br />(1982) analyzed across-section through the eastern portion of the present slide as unstable. The <br />I%- to 2-foot thick layer of soil developed over colluvium in the slide area indicates it had been <br />stable for a considerable period of time. <br />Past History of Local Landsliding <br />The history of landslides in the area is demonstrated by the following documented events: <br />Aerial photos taken in 1980 located in the CDMG files show numerous old dormant. <br />landslide features but no active slides in the vicinity of the Bear No. 3 portal. <br />In April 1986, a series of landslides and debris flows damaged Bear's access road and fan <br />portal. <br />A CDMG photo (June 1990) shows the western raveling slope being eroded by high river <br />flows. The two upper active landslides at the top of the November 1997 slide were <br />beginning to form. <br />Bears response to CDMG questions refers to a 1993 access road slide. <br />A CDMG photo (May 1993) shows the debris flow path west of the November 1997 slide <br />which runs into the westernmost raveling slope had formed. A small azea immediately <br />above the Beaz No. 3 portal had slid exposing bedrock. <br />831-032.411 Wright Water Engineers, Inc. Page 5 <br />