The Bay Area (including San Francisco) had quite a large modern day military presence up until recently. Treasure Island, BVHP, Presidio, Ft. Point, Ft. Mason, Ft. Funston, Ft. Cronkhite, Alameda, Moffett, Mare Island, Hamilton, Port Chicago, Oakland, Pt Molate, LLNL, Mt. Tam, etc., etc.
All of those saw active use during WW2, many up through the cold war. Letterman was used in every 20th century US foreign conflict. Sure, most of them were decommissioned during the Clinton era. But if it only took three decades to bring back segregation perhaps the military didn't bring lasting integration in the first place.
And if you look beyond the military towards support folks, the Bay Area saw a huge influx of immigrants during WW2 (e.g. for ship building). One look at Marin City and you'll notice the white immigrants got out ASAP.
Quite frankly I'd be careful calling San Diego "integrated". Perhaps the city proper is, but in my experience the burbs aren't necessarily (especially the more posh ones). Once you hit north county it turns in to duelling banjo country right quick. They don't call it Klantee without reason.
Met an individual while mooring a boat at the Berkeley Marina who was kind of a Bay Area time capsule.
He grew up on a houseboat in Sausalito, during WWII, and mentioned while the parents were working at the shipyards the kids would all go to a big gym and watch from a projector. Think they were given warm milk too.
He has a few stories that make Marin/East bay seem so small town. Times before the Richmond-San Rafael bridge.
The Bay Area used to have a large ferry system as well so suppose ship building makes sense.
To be fair, even a heavily segregated city like Chicago seems to be devoid of other races in black neighborhoods, but everywhere else the neighborhoods are pretty well integrated, including black people in those neighborhoods.
While I've family in both Chicago and San Diego it's been a much longer time since I've visited Chicago. So it's much easier for me to point out that SoCal (e.g. Surf City and Santee) has struggled with neo-nazis for a long time than it is for me to comment on the midwest with much authority. Although to be fair, it's a Chicago relative that got written up by the Tribune for being obscenely racist and violent.
I don't think it's particularly reasonable to paint black neighborhoods as uniquely or even inherently segregated. One of the things I loved about Oakland was how diverse it is across pretty much any criteria (economic, cultural, gender, racial, etc.). Even in the hills. And that's something sorely missing from San Francisco (and most parts of the Bay Area).
Someone (upper manhattan born and raised) once commented to me that they felt New York City was quite segregated. From their POV whatever integration you see is a result of folks commuting for (typically service industry) work. At the end of the day they'd just return home to their segregated communities.
