Prospecting for Hot Water in a Sedimentary Basin: Assessment of the Low-Temperature Geothermal Resource near Loma Linda, California

Abstract

Two sites for drilling intermediate depth geothermal wells have been identified near Loma Linda, California. Hot waters are ascending from the fractured crystalline basement complex along fault zone in this region. The primary well site is on a structural block (s) directly northwest of the city between the San Jacinto fault system and inferred trace of the Loma Linda fault. This well should encounter 45-65°C mixed geothermal waters in aquifers deeper than 700 ft. within Quaternary older alluvium. Penetration of the crystalline basement complex by this well at depths >1200 ft. may yield waters with temperatures as high as those issuing from the basement complex at Arrowhead Hot Springs at >80°C. A second exploration well is to be drilled just up gradient of the inferred trace of the Loma Linda fault zone south of the Santa Ana River. A >1600 ft. deep well at this site could produce waters >80°C from a geothermal plume ascending along shear zones in the basement complex. This well is expected to encounter 60-70°C aquifers at depths >700-800 ft. A third, alternate well site is located east of Loma Linda in the mouth of San Timoteo Canyon. A fault at this location is thought to be leaking hot waters into relatively think sediments and producing highly mixed geothermal waters with temperatures of 40-60°C. Data from these wells will be invaluable for exploiting the low temperature geothermal reservoir at Loma Linda.