Born & raised in San Francisco, I now live in Humboldt County (and I still go to the city at least once a month).
The Bay Area of course is an extension of San Francisco, I always felt as I was growing up, free and politically aware, I never understood the up-tightness of the rest of the country, from watching TV and reading print media, which is what all there was back then...
I think it's all evolved and SF has always been (and still is) a strong Union town, that's spead all across the Bay Area and the North Coast...SF has always had some degree of tolerance, since the Spanish settlers illegally traded with the Russian settlers across the SF Bay, and to the 49ers and Bowery days in SF, to the beats in the fifties, to the anti-war movement at SF State (and Berkeley) in the 60's---the music, the arts, the influx of people who givin up and came here to SF for a bit more freedom, the huge. mostly poor black population in Oakland, needed some militancy,(Black Panthers) citizen's being oppressed by the state and the local police. The laid backness of Marin and the huge working class growth of the South Bay...has helped evolve the Bay Area it's own shelted "bubble".
The beauty of San Francisco itself (and the Bay Area that feeds off of it) promotes a mellowness, tolerance, a feeling almost as an island onto itself, the Pacific Ocean, the mildness of it all...
I mean, Hawaii is probably more liberal than California...and Oregon is getting a huge native Bay Area migration and it's evolving more liberal, very fast, and so is Washington, only a bit slower...
When I just turned eighteen and voted for McGovern in 72...I never looked back and I now live in THE "liberal bastion" of the beautiful redwood coast, and the six rivers of Humboldt County!!!