This digital data set defines the boundary of the southwestern Nevada volcanic field (SWNVF), an area of thick, regionally distributed volcanic rocks within the Death Valley regional ground- water flow system (DVRFS), a 100,000-square-kilometer region of southern Nevada and California. The SWNVF boundary encompasses an approximate 12,000 square-kilometer region and is based on a map of hydrogeologic controls on ground-water flow by Laczniak and others (1996). The SWNVF is characterized in part by a thick section of regionally distributed welded tuffs derived from a central complex of nested calderas that erupted from about 16 Ma to 5 Ma. The SWNVF boundary defines the extent of these particular volcanics and was used to distinguish material property zones in the DVRFS. These zone arrays are used as input to the DVRFS transient ground-water flow model, a regional-scale model developed by the U.S. Geological Survey (USGS) for the U.S. Department of Energy (DOE) to support investigations at the Nevada Test Site (NTS) and at Yucca Mountain, Nevada (see "Larger Work Citation", Chapter A, page 8, for details).