Moving to California, buy a car there or bring one?

At the end of October I'm going to be moving down to the states on a TN Visa for a 3 month contract. I'm hoping get hired and end up staying for longer, but the only guarantee right now is the first 3 months.

I'm from B.C and was planning on buying a car here to drive down, just so I would have it right away.

My question is should I buy here, and if so how long do I have in California before I have to register it locally, and how much of a hassle is this?

My other option would be to buy a car in California. I've been told this would save me some headaches, however if I end up being down there for just 3 months it would be just as much of a headache to bring it back to Canada, and I may not have had to register it locally had I brought a car from Canada.

Sorry in advance if this is a bit of a repost and thanks for any suggestions