During the late Pleistocene the valleys of western Nevada contained large lakes of the Lahontan system. "Lake Dixie" was a 70 meter deep lake that filled Dixie Valley, a 30x90 kilometer valley one mountain range east of Lake Lahontan itself. An isotope and chemical hydrologic investigation of Dixie Valley and its adjacent mountain ranges indicates that virtually none of the valley groundwater present today could have recharged within the mountains. This is contrary to the commonly held belief regarding Great Basin recharge. Radiocarbon ages and ²H/H ("dD") ratios indicate that almost all of the groundwater in Dixie Valley was recharged between 14,000 and 30,000 years ago. This includes waters sampled at >3 kilometers depth, some which are of sufficiently high temperature to be used for geothermal energy. Regional geothermal gradients require that these waters have circulated to even greater depths, 5-6 kilometers, to gain their present temperatures. One of the most unusual features of Dixie Valley groundwater, required by ³⁶Cl/Cl systematics, is that it recharged as very dilute surface water ([Cl]<25 ppm). In contrast, groundwater recharged in the adjacent mountain ranges and most groundwaters recharging today in semi-arid to temperate regions, become substantially nondilute as they infiltrate downward through unsaturated soils ([Cl]>>50 ppm). This is because they incorporate chemical components ("salts") that have previously built up in the soils due to evapotransporation. Given the dilute origin of Dixie Valley groundwater, the fact that such water occurs uniformly throughout the valley, and its late Pleistocene age, we believe recharge had to have been predominantly through the bottom of Lake Dixie. The constantly saturated condition of the lake bed prevented evapotransporative salt buildup. The effect of Lake Dixie was therefore very substantial: lake water not only migrated to the 5-6 kilometer depths required for geothermal heating, but is also found in virtually all shallow wells and cold springs throughout the 90 kilometer long valley. If such recharge occurred throughout the Lake Lahontan system, as seems plausible, the late Pleistocene lakes of the western Great Basin had a significant lasting impact on regional hydrology.