It really depends on where you decide to live. California in general was designed around people getting everywhere by cars. Especially the Bay Area, which is basically suburbs which suddenly became the Tech Center of the world. Like others have mentioned the downtown areas are pretty walkable: I visited a friend in Mountain View and there were so many bars/restaurants downtown, there was always something to do once you parked and started walking (granted, there weren't quality nightclubs, but that might just reflect the demographic of the city). And the train station is nearby too.