Seems there are at least a few here that travel to California from time to time. Not posting any particular link because I can't find any 2 that jive completely. Examples though include:
Face to face sales through licensed dealers only
No ammo brought into California from out of state
BGC for ammo purchases
Permit, at some point (2019) will be required

Sorry not to post any links but the info doesn't seem, that I've seen, to have a general consensus.