I live in san leandro, I don't know of a club here but I have met a guy last year who told me about that club, I cannot find the info he gave me (we were both detecting and ran into each other) I wanted to call but never did because I had a hunting buddy for almost two summers and we went everywhere, he worked for the parks and got laid off, (illegal help was cheaper I guess).
Just don't make mess and clean up after yourself, the public parks are safe to hunt, I hunt them a lot. pm me if you are around here if I am not working I will hunt with you but I will only be around here for another few weeks or so. (gotta get ready for what this country is going to turn into) HH