Bay Area Hackers' Association / Bay Area Security Enthusiasts
BAHA/BASE is the "hacker hacker" security hacking subgroup of Bay Area Hackers' Association, as the hacker community includes many kinds of technical wizardry other than security stuff.
I formed the Bay Area Security Presentations mailing list to help reduce the cost of arranging speakers or finding venues.
I also formed a speakers mailing list to ping people who have offered to speak.
There is a Reddit for SF/BA security
We differ from these groups in that we are presentation and learning oriented, rather than primarily social.
It's not clear that the last two are active, since they don't seem to have much of a web presence.
We differ from OWASP Bay Area in that we discuss more than just web security.
There is a very similar group, DC650 (DEFCON Silicon Valley).
There is also the San Francisco 2600 group.
There is also a West Coast Hackers group.
And there's a SF Bay ISSA group.
North Bay and Seattle have Negative 9, which also appears similar to ours.
We are loosely based on Austin Hackers Anonymous, of which I was once a member; however, unlike AHA, I do not want to require people to have to present in order to attend.