Firstly, I don't need to tell you, but get the hell out of southern california. I think they should be two different states, and I'm very partial to the northern half. Go north and find some nature!
Yosemite, Tahoe, Shasta, Mendocino coast, the Redwoods!, Pt. Reyes.
San Francisco is pretty blown up but it's still an amazing city. Berkeley is pretty cool. Avoid Sacramento if you can.
Some of my favorite, really cool, small towns to visit are Inverness, Sebastopol, Bodega Bay, Guerneville.
All pretty general tips but like I said, start by going north and I'm sure you will find something that catches your interest. It's hard to go wrong north of SF, but I like to avoid Lake County, too many tweakers.
Hope this helps.