Where is the nearest public land for shooting to east Contra Costa County Ca. ?

Ok, I know that (with certain exception) that I can shoot on all BLM land, as well as in any national forest. I'm not so sure with national parks or state parks. However the nearest national forest to me is Stanislaus, and I'm having a hard time making heads or tails of where BLM land actually is. I live in the town of Brentwood, in contra costa county and would just like to find the closest public land (that is accessible by road). If you don't know of any, but know where I could find out that would be appreciated as well. (the BLM website didn't seem to be too helpful with specifics).