Approach to Geologic Hazard Zoning for Regional Planning, Inyo National Forest, California and Nevada

Abstract

The Inyo National Forest (the Forest), which occupies 3,000 mi 2 (7,770 km 2 ) in eastern California and western Nevada, is adminstered by the U.S. Forest Service (USFS). The uses of this national forest are primarily recreational, and as population in the region increases, the Forest will experience more intense use. This results in the need for additional roads, trails, camp-grounds and related facilities within the Forest. The most recent episode of strong earthquake activity occurred between 1978 and 1981, and caused an estimated $1.5 million in damage in the Forest area. In addition, seismically induced rockfalls caused at least nine injuries in and near the Forest. This earthquake activity and subsequent volcanologic studies were an impetus for the USFS to commission an evaluation and zoning of geologic hazards within the Forest for the purpose of land-use planning. The geologic hazards evaluated and zoned were limited to seismic hazards, slope instability, and volcanic hazards. Methods used included air-photo interpretation, literature review, consultation with selected geologists and volcanologists, and limited field reconnaissance. The study resulted in compilation of separate geologic hazard zoning maps at a scale of 1:24,000 for the three categories of hazards (seismic, slope instability, volcanic). The study concluded that slope hazards are of the greatest importance; seismic hazards are of moderate importance; and volcanic hazards are of the least relative importance. The hazard zoning maps and the accompanying report are now being used by the U.S. Forest Service planners for siting new facilities in lower risk areas, and for risk management.