Chances are you can't. If you send money you probably won't see it again or a key. If you really believe this is legitimate, have someone you know in California meet and verify who this person is and handle the exchange in person.
I had a listing cloned and posted as a rental that wasn't. They created an email like ChristoherKittrell@XYZ.com, with a legitimate mail host, but it wasn't my client. It was the scammer.
Please do whatever you can to protect yourself, the odds are not in your favor.