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INTRODUCTION <br />• ARCO Coal Company is planning a longwall mining operation at Jumbo Mountain neaz <br />Somerset in Gunnison County, Colorado. Plans are to mine the 'B' seam which is part of the <br />Lower Coal Member of the Mesaverde Formation. The strata in this area dip north-northeast <br />at two to five degrees. A lazge landslide deposit has been identified in close proximity to the <br />azea proposed for mining. The landslide deposit occurs on the north slope of Jumbo Mountain <br />in the valley of the North Fork Gunnison River. <br />-- This report addresses the nature and extent of the landslide deposits. It also discusses the <br />-potential for further landslide movements with or without mining. <br />SCOPE OF INVESTIGATION <br />The findings of this report aze based on the following scope of investigation: <br />• Review of aerial photographs taken in 1974 and 1992. <br />• Aground reconnaissance of the landslide. <br />• Review of the results of coal exploration drilling. A total of 45 boring logs were <br />reviewed from four different drilling programs. These were: <br />- CSM borings (1963): 26 <br />- MG borings (1981-1982): 5 <br />- CP boring (1982): 1 <br />- ]MB borings (1992): 7 <br />- JMB borings (1993): 6 <br />• Preparation of cross-sections, an isopach map of the landslide deposits, and a map <br />showing structure contours of the base of the landslide deposits. <br />RESULTS OF INVESTIGATION <br />The results of our investigations are provided in terms of: <br />• -1- <br />0:\Off\30\JPT\ARCO-Rpt.lkl <br />