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Memo to Boulay Jumbo Mountain Landaliding page 6 modern (since white man's occupation) activity. In several areas, predominantly in the middle to higher portion of the landslide mass, closed extensional troughs are present. These undrained graben-like topographic troughs are caused by downslope movement of landslides pulling away from the upslope headscarps. The most impressive of these features examined measured approximately 30 feet across and twenty feet in depth, extending for a length of approximately 100 feet. Several of these troughs have been the locus of "natural" stock watering ponds. Unfortunately, this practice provides infiltration water on the landslide mass, which is not conducive to stabilization of the landslide materials. One such pond is referenced by Mr. Mautz as having been dewatered by the 1996 landslide. Judging from the size of tree growth and the degree of smoothing by weathering of the graben side slopes, I estimate that these larger features are in excess of a century in age. I also examined several smaller troughs with widths of five to ten feet and depths in the five foot range. These smaller grabens were less weathered, retaining smoothed but steep-sided trapezoidal shapes, and were less vegetated with small aspen saplings and scrub oak, suggesting ages of several decades. While these estimates of age are based on my experience and may be grossly flawed, the comparative age of these features and the active landsliding demonstrate that recurrent episodes of landsliding have affected this area, separated by periods of relative stability. Subsidence Cracking on Jumbo Mountain At several locations during my 1996 and 1997 tours of the site, I examined cracking which appeared indicative of subsidence troughing without landslide translational movement. These cracks are generally limited in width (2 to 6 inches), and demonstrate no translational or lateral offset between the opposite faces of the cracks. Their orientation tends to sub-parallel the axis of the panel or the longwall face. In contrast, landslide cracking is prolific throughout much of the Jumbo Mountain north slope, contrastingly characterized by extensive translation and offset across crack planes. Relationship of Subsidence and Landslide Occurrence Because of the proliferation of landslides throughout the North Fork valley, the Division has repeatedly expressed a concern regarding the possible reactivation of ancient, historic and modern landslides by subsidence during mine permit review. This same concern is commonly expressed by land owners and the public. The Division has included permit conditions requiring every mine with mapped landslide deposits above projected subsidence to monitor the