Preliminary map showing recently active breaks along the Maacama Fault zone between Hopland and Laytonville, Mendocino County, California

The southernmost 15 km of this map is a product of a study that began in 1975 as part of a study of recency of faulting in coastal California (Ziony and others, 1974; Buchanan-Banks and others, 1978; Pampeyan , 1979). In February 1975, after being shown evidence of recent faulting in the vicinity of Ukiah by E. C. Winterhalder, Principal Engineering Geologist for Harding - Lawson Associates, Pampeyan extended the study area northward to the vicinity of Willits . After the Willits earthquake of November 22, 1977 (Simon and others, 1978; Warren and others, 1979), field investigations in the epicentral area revealed a series of distressed pavements, curbs, and sidewalks all showing right-lateral offset (Harsh and others, 1978; 1981). These features traverse the city of Willits and define a line coincident with a photolineament extending southeastward from Willits. Subsequently, additional sites of distressed pavements discovered both east and north of Ukiah alone; other lineaments of the photogeologic study verified the existence of tectonic creep in the Maacama fault zone.