This report presents the results of geothermal resources investigations conducted in the Sonoma Valley area of California by the California Department of Conservation's Division of Mines and Geology. Included are the results from separate studies performed in two preceding years, of the southern and central Sonoma Valley area (1981-82) and the northern Sonoma Valley area (1982-83); also included are the results of a shallow temperature drilling program and general "wrap up" assessment of the resource conducted in 1983-84. 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.

This addendum report presents the results of the California Division of Mines and Geology (CDMG) drilling program at Calistoga, California, which was the final geothermal-resource assessment investigation performed under terms of the second year contract (1979-80) between the u.s. Department of Energy (DOE) and the CDMG under the State Coupled Program. This report is intended to supplement information presented in CDMG's technical report for the project year, "Resource Assessment of Low-and Moderate-Temperature Geothermal Waters in Calistoga, Napa County, California."