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Memo to Boulay & Berry <br />Bear 111 Landslide <br />page 5 <br />of the North Fork of he Gunnison River. Examination of the upper slope discerns numerous and <br />extensive landslides and debris flows. Approximately 500 feet up slope from the Bear III <br />landslide an extensive complex of debris flows blankets an upper surface. These flows break <br />over the crest and flow down the exposed hillslope in several locations adjacent to the Bear III <br />landslide. Several lazge scale (up to 50 foot high) head scarps bound the up slope terminus of <br />these flow complexes. Older flow deposits mantle these head scarps in at least one location. The <br />superposition of these deposits provides insight into the sequence of their formation. <br />Examination of the 1980 aerial photography determined that the hillslope had apparently been <br />stable for at least several centuries. In the area of the landslide in excess of one toot of multiple <br />horizoned humic topsoil covers the slope uniformly. This soil mantle may have taken several <br />millennia to develop. Mature trees and scrub Oak veneer the slope. Grass and scrub oak covers <br />the majority of the North Fork valley side slope with the exception of several rock ledges. <br />During the El Nino year of 1983 slope failure at this site resulted in extensive damage to the fan <br />portal facilities at the Bear III mine. The extensive flow complex up slope From the Beaz III slide <br />was reactivated at that time. Subsequent landslide and debris flow events have occurred <br />repeatedly during the past 14 yeazs. <br />Aerial photographic evidence suggests that the headscarp of the modem debris flow complex <br />may represent a penetrating failure plane of an older large landslide. This larger landslide may <br />have involved bedrock beneath the colluvia] cover. The juxtaposed debris flow deposits which <br />cross and cover this large scarp may provide evidence relating to the length of time this scarp and <br />landslide have remained relatively stable, The muted form of the flow deposits, the maturity of <br />soil and grass cover, and the lazge size of mature conifers suggest that this scarp and large <br />landslide, if it exists, have remained stable for a minimum of several centuries. <br />During our field examination on Febmary 10, 1998, both Bruce Stover and I attempted to <br />examine portions of this upper scarp and mudflow complex which I hypothesize might provide <br />telltale evidence to verify or refute the existence of lazger, deeper-seated failure planes. Snow <br />cover and field conditions prevented us from completing the necessary examination of the <br />suspected telltale locations. <br />Conclusion <br />It is my opinion that the November, 1997 landslide which occurred adjacent to the recently <br />reclaimed Bear III mine portals was initiated by groundwaters emanating from the bedrock <br />beneath the failed colluvium. Observations of the slope geomorphology, stratigraphy of the <br />colluvia) deposits, and pedologic development suggest that the initiating groundwater discharge <br />is a new phenomena or changed condition, which has not been occurring for any significant <br />