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Memo to Boulay Jumbo Mountain Landsliding page 2 Previous Analysis for MCC - Dames and Moore, 1993 In 1996, and again after the August 21, 1997 inspection, I reviewed a 1993 report prepared by Dames and Moore, entitled "Landslide Investigation Report, Jumbo Mountain, Somerset, Colorado for ARCO Coal Company". MCC commissioned this investigation while planning their 'B' seam longwall operations beneath Jumbo Mountain. Dames and Moore investigated a large landslide complex on the north slope of Jumbo Mountain. A portion of this 500 acre landslide complex subsequently became reactivated during the spring of 1996, damaging a road and small stock watering pond on the Mautz property. Again, in the spring of 1997, a separate portion of the large pre-historic landslide became reactivated, spalling the facial slope of Muffler Rock. The Dames & Moore investigation, based on the analysis of extensive boring logs of the Jumbo Mountain Tract, concluded; "Landslide deposits exceeding 100 feet in thickness were penetrated by borings located through a bench or terrace which occupies a zone up to 2,000 feet wide between the 6,620-foot and 6,850-foot contours (figure 1). These landslide deposits are underlain by the lower part of the 'B' seam suggesting that a bedding plane or parting in this seam formed the base of major slide movements. The 'B' seam outcrop, therefore, represents the downslope limit of landslide deposits. These deposits clearly represent the remnant of a large ancient landslide." Dames and Moore mapped this landslide as exceeding 500 acres in area, and exceeding 148 feet in thickness. Dames and Moore further observed; "There is no evidence of current instability on the lower, bench portion of the landslide. In fact, the lack of any surface evidence of past movement indicates that this area has been stable for a long period. Scarps up to 12 feet high are present in the upper, steeper south part of the landslide mass as shown on figure 1. These scarps indicate recent movement. The largest of these scarps are evident on both 1974 and 1992 aerial photographs. This indicates that sliding is occurring slowly - probably less than one foot per year of overall downslope movement." My examination of the two subsequent episodes of cracking and landslide movement which has occurred does not refute any of Dames and Moore's conclusions. Investigation of Jumbo Mountain landslides - Richard Dunrud, 1997 MCC recently contracted Dr. Richard Dunrud, retired USGS, to complete a field investigation of the Jumbo Mountain landslides, including the