The area examined in this report is located in the extreme southwestern corner of Arizona, principally in the Sonoran Desert subprovince of the southern Basin and Range province. A very small portion of this corner of Arizona lies within the Salton Trough subprovince, a deep sediment-filled structural depression that trends northwest through Mexico, Arizona, and California. At least a dozen geothermal anomalies have been identified in the Salton Trough (Elders, 1979). The geothermal anomalies are generally located above segments of the East Pacific Rise, an oceanic spreading center that extends up the Gulf of California and beneath its landward extension, the Salton Trough. The region is interpreted as a complex, transitional plate boundary that takes up stress created by two different tectonic regimes: spreading at the East Pacific Rise and transform motion along the San Andreas fault system as the Pacific plate moves northwestward. As a result of this continuing motion, the Gulf of California- Salton Trough system is a actively growing rift. (27 pages)