Along the back roads north of Stockton there are geodes in ditches and farms. I've only seen small druzy quartz and calcite crystals in the ones that I've cracked so far. Some of it is botroydial and some is iron-stained. I've heard of pyrite and sphalerite spotted in some, but I don't know. There is also fossilized coral (horn and other) there. It's best to search the creeks, gravel bars, eroded farm soil, and road ditches in the area. I would recommend asking a livestock farmer if you can remove some of the pesky geodes for them since they can be harsh on cow ankles.
My reference is from the NWA Gem and Minerals club, but I did not disclose our exact location.  This information was repeated from my source at http://gemstone.smfforfree4.com/index.php/topic,2403.0.html (look for hulagrub's post on page 1).