This report presents the results of an investigation, by the California Division of Mines and Geology, of the geothermal resources of the northern Sonoma Valley area, California. A report on the geothermal resources of the southern Sonoma Valley area, (Youngs and others, 1983) indicated several patterns, trends, and anomalies that appeared to extend north and northwest in the valley. Study of the northern valley area was conducted to attempt to follow these trends and to determine whether significant geothermal resources exist in the area.