This report presents the results of the California Division of Mines and Geology's (CDMG) geothermal resource investigation of the Sonoma Valley area, California. The study was undertaken to learn more about the known low-temperature (20°_90°C) geothermal resource in this area and. to assess the potential of the resource for development and use by the local community. The project was conducted in compliance with the terms of the fourth-year contract (1981-82) with the U.S. Department of Energy (DOE) under the state-coupled program and performed under CDMG's Phase II site-specific geothermal resources studies program.