You can indeed. There are no counties that prohibit open carry because state law preempts county and municipal governments from declaring something unlawful which state law explicitly says is lawful. Watch out for K-12 schools, read the newbie thread, read the info at californiaopencarry.org, watch pullnshoot's videos, take the quiz.
Be careful out there. Don't talk to cops. Don't carry ID. Be polite. Keep your mags holstered and visible. And seriously, watch out for those K-12 schools.