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Memo to Houlay <br />Jumbo Mountain Landsliding <br />page 3 <br />"Muffler Rock" landslide. Dr. Dunrud is a nationally recognized expert <br />in the field of subsidence mechanics, which was one of his primary topics <br />of expertise during his long career at the United States Geological <br />Survey. Among his numerous publications, Dr. Dunrud authored several <br />USGS monographs addressing subsidence mechanics in Somerset, Colorado and <br />the Book Cliffs areas. Following our inspection, MCC forwarded a copy <br />of Dr. Dunrud's DRAFT report for my examination (see attached). <br />In addressing the landslide at Muffler Rock, Rich Dunrud concludes; <br />"Though the slide this spring at Muffler Rock was roughly coincident <br />with the movement of the Panel 9 longwall face beneath it, it is <br />unlikely that the mining influenced the slide movement <br />significantly. The Mesaverde sandstone and overlying surficial <br />material moved northward during the slide; the Panel 9 longwall face <br />moved eastward. The tilt, curvature, and strain produced by <br />longwall mining (and attendant subsidence) would be maximum in the <br />east-west direction and minimum (or perhaps zero) in the north-south <br />direction. Therefore, I believe that the predominant cause of the <br />slide at Muffler Rock this spring (1997) was the saturated <br />conditions of the material and the northward dip of the bedrock <br />(about 5 degrees) towards the currently existing Muffler Rock <br />landslide scarp." <br />Reexamination of the Jumbo Mountain north slope Landslide Complex - 1996 <br />Deposits <br />During spring of 1996, approximately 30 to 50 acres of the SW1/4 of <br />Section 24 was affected by landsliding. Mr. Mautz reports that minor <br />cracking was noted by his ranch hands on the roads within the affected <br />area in the fall of 1995, followed by extensive landsliding in May / June <br />of 1996. This is in keeping with my observations of annual spring/summer <br />landsliding in the North Fork Valley over the pasC nineteen years. <br />Cracks and graben-like (steep-sided trapezoidal) extensional troughs up <br />to ten feet wide and five feet deep were examined in several locations <br />towards the middle to lower portions of the landslide deposit. The more <br />common features are cracks 3 to 12 inches in width. Cracks can be traced <br />for lengths in excess of 100 feet. Most cracks evidence translational <br />offsets indicative of downslope and lateral movements. Cracks occur <br />along contour, parallel to the fall line, and at random orientation. No <br />discrete conclusions could be made about the actual depth of the basal <br />failure plane of the landslide mass(es). The features I observed are <br />typical of large landslide masses in the Williams Fork formation of the <br />Mesaverde Group. These landslides occur prolifically throughout the <br />