Read up at www.californiaopencarry.org
If you don't stop for gas, unloaded and exposed while in CA. The only thing you have to worry about is "Gun Free School Zones." The law exempts you if you don't "reasonably know" you are in a GFSZ, but that might not stop a conviction.
If you want to be 100% in the clear, just keep it unloaded and locked in a secure container. I'd keep it on the seat next to you just in case you need it.