Contemporary seismicity in the northern California Coast Ranges from San Francisco Bay to the town of Healdsburg and east of the seismically quiescent North Coast segment of the San Andreas fault is generally confined to the intensely deformed Santa Rosa block relative to the adjacent Sebastopol block. Much of this activity is concentrated along the Rodgers Creek, Healdsburg, Bennett Valley, and Maacama faults. A prominent gap in microseismicity exists along much of the 43+ km-long Rodgers Creek fault, although paleoseismological evidence suggess that the fault has generated at least three paleoearthquakes of moment magnitude (Mw) 7 or greater during the late Holocene (Budding et al., 1991). Earthquakes in the region are generally confined to upper crustal depths of less than 10--12 km. Right-lateral strike-slip faulting on both northwest and north striking faults is currently the primary mode of regional crustal deformation based on observed focal mechanisms, although both reverse faulting, especially in the vicinity of the major Quaternary faults, and normal faulting occur within the region. The tectonic stress field in the region is dominated by north-northeast to northeast directed compressive stresses. Although the Rodgers Creek fault may pose the highest known level of seismic hazard in the region in the next few decades, abundant geological evidence and the contemporary seismicity suggest that faults such as the Healdsburg, Bennett Valley, and Maacama faults also pose significant hazards because of their potential to generate Mw 6--7¿ earthquakes. ¿American Geophysical Union 1991