Fort Tejon earthquake strikes Central and Southern California

Background. The earthquake occurred on the San Andreas Fault, a continental right-lateral strike-slip transform fault extending through California. The southern section of the fault, where the rupture occurred, accommodates displacement between the North American and Pacific plates. The event is named after Fort Tejon, a former U.S. Army outpost in Kern County, although the epicenter was nearly 100 miles away from the fort.

Magnitude and Rupture. The earthquake had an estimated moment magnitude of 7.9, making it one of the largest recorded in the United States. The rupture extended for approximately 225 miles (350 km) along the southern part of the San Andreas Fault, specifically between Parkfield and Wrightwood.

Timing and Location. The event occurred at about 8:20 a.m. Pacific time on January 9, 1857. Local solar time was used in 1857, with San Francisco maintaining the most accurate time due to its status as a commercial center. The earthquake affected Central and Southern California, with the rupture centered in the southern segment of the fault.