Slope stability of proposed ski facilities at the southeast side of Snodgrass Mountain, Gunnison County, Colorado

Part of the proposed expansion of ski facilities at Crested Butte Mountain Resort, Gunnison County, Colorado, is in an area underlain by landslide deposits that are on the southeast side of Snodgrass Mountain. Except for localized movement, the landslides do not appear to be moving at present or to have moved in the past several decades. Shallow sliding and debris flows have occurred in similar materials nearby and are likely to occur in the landslide deposits during the 50-100 year life of the proposed facilities. Hazards related to debris flow, shallow slumping, and expansive soils in the deposits can be reduced by appropriate engineering and remedial measures but maintenance for the proposed facility may become costly. Snow making is likely to aggravate the hazards of shallow slumping, deep-seated sliding, and debris flow. Reactivation and deep-seated movement of a 1.6-million-m3 slide at the east side of the deposits would damage or destroy a proposed gondola, ski lift N-3, and related facilities. Moving the gondola and lift off the slide and prohibiting snow making on the slide will protect the gondola and lift and reduce the chances of debris-flow damage to a proposed development near the toe of the slide. Insufficient data are available to assess the current or future stability of the landslides or to evaluate possible mitigation strategies; detailed stability analyses are needed before developing any facilities on the landslide deposits.