In the 1960s, a major hydrogeologic investigation was conducted at the Nevada Test Site (NTS, Figure 1) that included drilling, hydraulic testing, and hydrogeochemical studies in conjunction with geologic mapping and geophysical surveys. This work demonstrated that a large part of south central Nevada is underlain by thick (several kilometers) highly fractured Paleozoic carbonate rocks that typically act as an aquifer. The aquifer flanks and underlies most of the intermontane basins from east central Nevada southward, through the NTS, to the southern Funeral Mountains east of Death Valley (Figure 1). Water levels measured in many test holes demonstrate that the potentiometric surface in the carbonate aquifer generally is uninterrupted by the ridges that separate the many topographically closed basins of the region. These findings have been interpreted as evidence that interbasin flow integrates Yucca Flat, Frenchman Flat, Mercury Valley (Figure 1), and other adjacent topographically closed basins, into a single groundwater basin tributary to the springs at Ash Meadows in the east central Amargosa Desert (Figure 1). In view of these findings―documented in great detail by Winograd and Thordarson <1975>, Laczniak et al. <1996>, and Thomas et al. <1996>―we are perplexed by Nelson et al.'s <2004> statement that the concept of interbasin flow may be fundamentally flawed or at least not as universally applicable as previously thought.