A combination of three independent lines of evidence (hydrogeological, geochemical, and isotopic) suggests that as much as 3.7 × 107 m3 per year of interbasin flow may occur through faulted and fractured bedrock in the southern Sierra Nevada. The proposed interbasin flow path is through fractured Sierran bedrock from the Kern River drainage basin (which supplies recharge to the San Joaquin Valley to the west) into the southwestern Indian Wells Valley, a desert basin that is east of the Sierra. The interbasin flow produces an amount of recharge that significantly increases the ground-water budget for the desert valley.
The interbasin flow is identified by aquifer flux values much higher than local recharge and by ground water that has geochemical and isotopic signatures that differ from the local recharge. Interbasin flow that crosses topographic watershed divides has been identified in fractured carbonate aquifers in the southwestern United States. However, igneous and metamorphic rocks in the Basin and Range province are generally considered to be flow barriers, and watershed boundaries are usually delineated by topography. In this study we present an example in which recharge appears to be transported between adjacent watersheds through the fractured bedrock of an extensional area in the southern Sierra. If confirmed, this example shows that igneous and metamorphic rocks may not always act as barriers to ground-water flow in extensional tectonic regimes.