I actually grew up in California until I was 13 and go back to visit as often as I can. I totally understand why you would want to stay. Have you decided where you are going in California?
Congrats! That is an amazing offer! Why are you going to have to turn it down? I am still waiting to hear about funding. Did they e-mail you recently? Do you know if the funding is from the Graduate School or the Social Work Department?