I too live in California, and I bought out of state. The 300C is 50-state legal. There is a sticker under the hood that has the emission status on it. To bring a 300C into California, you must get it smogged, even though it is a new car. The smog shop I took mine to had to fail the car, as their computer could not talk to the OBD2 computer in the 300C. It turns out that the connecter is changed, so only certain places can smog your car. This will change with time, of course. I had to pay a dealer $80 for a smog check :-(
To register it in CA, you need either the title or the manufacturer's statement of origin. This got mailed to me about 2 weeks after I got home. I was able to get a temporary CA tag, paying all the fees, and then when I received my origin statement and had the smog test done, I went back and got plates. Expect to pay tax up to the CA rate. I bought in Michigan, which has a 6% rate. When I went to the DMV I had to pay an additional 1.25% to bring it up to my county's rate. The 6% I paid in Michigan is apparently sent to CA. So, the process isn't as bad as some government crap, but crap is crap.