It's not like med school where they have to take mostly in-state people. However, I think there is some bias in favor of fellow Californians. At least you need to justify why they should take you, why you'd fit in living there and/or that you have some friends/family there, or other good reasons why you want to go there. I think for an average applicant it might be a bit tough, just because there are so many others from CA vying for the same spot, but a lot of this depends on the specialty you want, right? If it's family practice, IM or psych, if you are a strong applicant, the programs will want to compete over you regardless of where you are from.