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Evaluation of Bear No. 3 Mine Landslide <br />or stops in the late summer and fall. Examples of this occutred in the wet springs of 1985, 1986, <br />1987, and 1997 when many serious landslides occurred across western Colorado. <br />Locally, the North Fork has cut a deep, steep-sided valley through the Mesaverde bedrock. This <br />1 exposed the beds which dip 3 to 5 degrees to the north-northeast. Although minor low relief <br />folds and faults of a few feet displacement can be seen in the mine workings and outcrops, major <br />faulting or folding is not evident. <br />]n the Somerset area, colluvium of varying thickness accumulates below the sandstone cliffs and <br />in pockets of gentler slope. Thick wedges of colluvium accumulate against the old bedrock <br />surface where steep valley walls reach the flat valley floor. The interface between the colluvium <br />and the bedrock mimics that seen in outcrop slopes. At competent thick sandstones, the <br />interface is steep, almost cliff=like. When shales or soft beds occur, the surface is more gentle. <br />Alluvial gravels of sand and boulders occur along the North Fork and its tributaries. The Bear <br />No. 3 Mine facilities occupy a broad alluvial terrace. <br />Numerous authors-lunge (1978), GeoHydro Consulting (1980), Rocky Mountain Geotechnical <br />(1981, 1982, 1986, and 1996), Harding-Lawson Associates (1997), Dames and Moore (1993), <br />Intraseazch (1993 and 1994) and Rold (1994 and 1997) have studied slope stability in the <br />Somerset and Bear Mine area. All of them have mapped various types of landslides and slope <br />instability both east and west of the November 1997 Bear No. 3 landslide, but none except Rold <br />have shown landslide activity at the area of the present slide. Rold's September 1997 study <br />mapped three raveling slopes at the base of the slide and two small active landslides and <br />associated debris flows. The two landslides have grown to the November slide head scarp and <br />the three raveling slopes at the base have merged into the one very large basal raveling slope. <br />The aerial photo map of the Bear No. 3 Mine azea (Figure 1) shows the location of the numerous <br />landslides in the vicinity of the November slide. <br />831-032.411 Wright Water Engineers, Inc. Page 3 <br />