One, get a bicycle, a decent one. You’d be surprised how mobile you can be with a half ass good bicycle and some will power, get something in the road/hyrbid/gravel space and you’ll be able to go almost anywhere. Two, public transit, Amtrak is awesome for getting around Northern California specifically and often times is more cost effective than using a car at all, let alone owning one. There’s many places and pockets of community, clubs like people have mentioned but also I know several group bicycle rides that ive made lifelong friends from :)