If you have just one chance to hike in the San Francisco Bay Area, one of these destinations should be on it.
The North Bay is primarily Marin County, across the Golden Gate Bridge from San Francisco, and some of San Rafael County.
East Bay includes Contra Costa and Alameda counties.
South Bay encompasses the Santa Cruz Mountains south of San Francisco and Santa Clara County, whose hills border Silicon Valley.
What to bring:
Layers -- weather is highly variable
Water and snacks