1868 October 21 15:53 UTC
At 7:53 AM local time, on 21 October 1868, the destructive waves from a Magnitude 7 earthquake on the southern end of the Hayward Fault, quickly traveled across the San Francisco Bay Area and beyond. Because of its location in the heart of the Bay Area, then having a total population of about 260,000 (Federal Census records), and its magnitude, variously estimated as between 6.8 and 7.0, this earthquake was one of the most destructive in California history. Property loss was extensive and 30 people were killed. Five deaths were reported in San Francisco, out of a population of 150,000, where the total property loss was estimated to be $350,000 ($5-100 Million in 2007 dollars). This earthquake was known as the "great San Francisco earthquake" until the Magnitude 7.9 shock on 18 April 1906. The cracking of the ground along the Hayward Fault was traced about 20 miles (32 km) from San Leandro to Warm Springs in Fremont, although modeling of survey data suggest that the fault moved as far north as Berkeley, and from these data the average amount of horizontal movement along the fault is inferred to be about 6 feet (1.9 meters).
Damage was most severe in Hayward and nearby towns along the Hayward fault in Alameda County. At Hayward, then a town with about 500 residents situated on the Hayward Fault, almost every building was damaged extensively or wrecked. At San Leandro, a town of about 400, the second floor of the Alameda County courthouse collapsed, and other buildings were wrecked. At Mission San Jose, in southern Fremont, the old adobe church and other buildings were wrecked. San Jose, which lay in the hills several kilometers west of the fault trace, a town of about 9000 residents, had many wrecked buildings and demolished chimneys. Across the Bay, at San Francisco, the Custom house and several other structures built on landfill reclaimed from the former Yerba Buena Cove (today's Financial District), sustained severe damage, and many cornices, awnings, and walls fell, but, as occurred later in the shock of 1906, well-constructed buildings on firm ground sustained little damage. Damage in Oakland, having a population of about 12,000, and mainly wood frame buildings, was much less than observed farther south at San Leandro and Hayward.
Sadly, many of the engineering lessons learned from this earthquake and openly discussed at the time, such as the hazards of building on "made ground" reclaimed from the San Francisco Bay or the admonition to "build no more cornices," were long forgotten by the time of the 1906 quake.
Damage occurred from Gilroy and Santa Cruz on the south to Santa Rosa on the north. The area shaken at Modified Mercalli intensity VII or higher includes about 900 square miles (2,300 km2). Strong aftershocks continued into November 1868.
Modified and 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.