[en] This report contains data on ground-water levels and preliminary maps of the potentiometric surface beneath Yucca Mountain and adjacent areas, Nye County, Nevada. The information was obtained in cooperation with the US Department of Energy to help evaluate the suitability of the area for storing high-level nuclear waste. The water-level surface shown on the maps generally represents water-table (unconfined) conditions. The water table in the Yucca Mountain area occurs in ash-flow and air-fall tuffs of Tertiary age. West of the crest of Yucca Mountain, water-level altitudes are about 775 meters above sea level. Along the eastern edge and southern end of Yucca Mountain, the potentiometric surface generally is nearly flat, is about 728 to 730 meters above sea level, and has a southeastward slope. 2 references, 2 figures, 2 tables