Studies of the hydrogeology of the southern Great Basin differ widely in their conclusions regarding the origin of major springs at Ash Meadows, in the Amargosa Desert, Nevada, and in the Furnace Creek- Nevares Spring area in Death Valley, California. The diversity of opinion reflects the following. First, ground water commonly moves between intermontane basins of the region via thick, highly fractured, and areally extensive Paleozoic carbonate rocks; the resulting lack of correspondence of topographic and ground-water divides precludes routine utilization of the water-budget method in the study of these basins. Second, subsurface hydraulic data for the regional carbonate aquifer are sparse and difficult to interpret because of the complex subsurface disposition of and hydraulic barriers within the aquifer. An analysis of hydrologic, geologic, geochemical, and isotopic data permits a first approximation of the subsurface watershed tributary to the cited spring groups. Water temperature, chemistry, isotope content, hydraulic head, and geologic relations indicate that the major springs at Ash Meadows and in the Furnace Creek-Nevares Spring area, though emerging from unconsolidated Quaternary strata, are fed by water moving directly from the underlying carbonate aquifer of Paleozoic age. Joint use of potentiometric, geologic, and isohyetal maps indicates that the subsurface watershed tributary to Ash Meadows is no smaller than 4,500 square miles. The Ash Meadows ground-water basin is bordered on the south and east by the Spring Mountains and Sheep Range, the principal recharge areas, and on the west by the Belted Range, Eleana Range, and Shoshone Mountain. A northern boundary was not definable, and some underflow from White River ground-water basin, 90 miles northeast of the springs, is probable. The hydrogeologic data do not support the conclusion of earlier studies that underflow from Pahrump Valley is the major source of the spring discharge at Ash Meadows; probably no more than a few percent of the total comes from that valley. Comparison of the size, climate, and discharge from the Ash Meadows basin with that of the surface watershed tributary to the Furnace Creek-Nevares Spring area indicates that most of the spring discharge in east-central Death Valley originates well beyond its confines. Disposition of the carbonate aquifer favors the movement of ground water into Death Valley from central Amargosa Desert. Water in the carbonate aquifer in the latter area may be derived from the Ash Meadows basin, from the overlying valley fill, or both. Five hydrochemical facies were distinguished by percentage of major cations and anions in ground water from 147 sources. The hydrochemical facies reflect both the mineralogy of strata within recharge areas and downward crossflow from a Tertiary tuff aquitard into the carbonate aquifer. The areal distribution of these facies provides evidence for a northeasterly source of the Ash Meadows discharge, absence of significant underflow from Pahrump Valley to Ash Meadows, and movement of water from the central Amargosa Desert to the Furnace Creek- Nevares Spring area. The data are also compatible with southwestward underflow into the Ash Meadows basin from the White River basin. The deuterium content of 53 water samples from 27 major valleylevel springs and selected wells falls into several areally distinct patterns which suggest that 35 percent of the Ash Meadows discharge is derived from the White River basin, that underflow from Pahrump Valley is unlikely, and that water discharging in the Furnace Creek-Nevares Spring area may be related to water in the carbonate aquifer within the Ash Meadows basin. However, other interpretations are possible indicating that unequivocal interpretations about the regional flow system cannot be made from isotopic data alone.