The hydro geologic study area consist of three ground-water sub basins that re a part of the Death Valley ground-water basin. These sub basin are the Oasis Valley sub basin, Alkali Flat-Furnace Creek Ranch sub basin, and the Ash Meadows sub basin. The division into and the approximate boundaries of these ground-water sub basin have been estimated from potentiometric levels, geologic controls of subsurface flow, discharge areas, and inferred flow paths. In some areas, the boundaries are uncertain due to the lack of potentiometric data, the complexity of geologic structures, of the occurrence of interbasin flow of ground water through the lower carbonate aquifer. Regional flow paths in the hydro geologic study area vary in directions from southerly to southwesterly. Detailed discussions of the regional hydrogeology and regional flow systems are included in Section 3.6 and 3.7. Detailed discussion of the site hydrogeology are included in Section 3.9. The Discussions include aquifer hydraulics information, water-balance calculations, and water-chemistry data for both the saturated and the unsaturated zones.