Here's some resources for you: There's 3 montly brick & mortor clubs (that I know of), in your area. There's the San Jose club (http://waipahuhaole1.tripod.com/treasurehunters.html), then there's a club in Concord (don't know their monthly times, etc...), and a club in San Bruno.
As for regional specific forum, there's the kinzli forum (which is what I think jerr696 was alluding to). Several bay area folks chime in there.
I'm in Salinas, but love to hunt SF parks whenever I get up that way. As built up as SF is, yet there's oodles of grass and green belts interspersed in the urbran sprawl. Various old-town demolitions have produced some fun hunts.