On October 21, 1868, a powerful earthquake occurred along the southern extension of the Hayward fault in the east San Francisco Bay Area. The quake measured about M 6.8 and causes extensive surface fault ruptures from Castro Valley to about Coyote Creek in Milpitas.

The quake shook many towns in the East Bay quite violently, with relative shaking intensities of X on the Modified Mercalli scale (a relative shaking intensity rating from 1-12 shown in Roman numerals).

The most severe damage occurred in Hayward, where nearly every building suffered extensive damage and many structures were completely wrecked. In San Leandro, the courthouse and jail collapsed, and damage was reported as far away as Santa Cruz, Gilroy, and Santa Rosa.

Thirty deaths were attributed to the event. A strong aftershock sequence lasted for several for years.

Almost three years earlier to the day, October 8, 1965, a M6.5 quake struck the eastern foothills of Santa Clara County. This earthquake also caused substantial damage.

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