There may be a show coming up later in the summer--I'm not sure. What you can do is go to the AKC website www.akc.org and look at the column on your left. There'll be a header that says 'Events search'. Click on that, and when the map comes up, select CA, and enter 'Basset' in the show name. Then select conformation--that'll get you the most AKC Basset Events, because all of the clubs have conformation shows, but not so much the other stuff.
On July 4th, Northern CA has BAsset WAddle in Petaluma, but that's 'north'.