Gnarwhl, the only beaches in the San Francisco area that are supposedly off-limits, is any federally administered beaches. That would be : Any under the GGNRA domain. All the others are okay. You can see the boundaries on maps for which beach is under what public entity.
And I say "supposedly ", because: There's been a few humorous incidents of persons who simply didn't know any better. And they went for months or years, and nobody ever said so much as "boo" to them. And another guy who was trying to do a posse search for a lady who lost a gold ring. He fretted himself silly about how he was going to do it. In the end, he just went. Figuring that, after all, he was doing a legitimate search. No problem for him either. But that's a different subject for a different thread.