1966 June 28 04:26 UTC (local time June 27)
This earthquake occurred in a sparsely populated region near Parkfield, so little building damage was sustained. The main damage included broken windows, cracked walls and swimming pools, and overturned tombstones in the Parkfield cemeteries.
Minor surface faulting, about 35 km long, occurred in a narrow zone along the San Andreas faultfrom a few kilometers northwest of Parkfield almost to Cholame. About 1.5 km northeast of Cholame, the white dividing line on Highway 466 was offset about 10 cm. At that same site, a small concrete bridge sustained minor cracks and the pavement buckled. Bridges on the Parkfield-Cholame Highway, which parallels and crosses the fault trace several times, sustained minor damage. It was felt generally from Santa Cruz to Oxnard and northeastward into the Sierra Nevada foothills. It was preceded by a strong shock at 04:08 UTC on June 28 and followed by shocks of lower magnitude on June 28 and 29. More than 200 aftershocks occurred through December 1966.
Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.