These contours represent the simulated potentiometric surface at the end of simulation (1998) in model layer 16 of the Death Valley regional ground-water flow system (DVRFS), an approximately 45,000 square-kilometer region of southern Nevada and California. The numerical ground-water flow model simulates prepumping conditions before 1913 and transient-flow conditions from 1913 to 1998 after pumping of ground water began. The DVRFS transient ground-water flow model is the most recent in a number of regional-scale models 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).