I imagine that most folks simply check into a motel, or stay with friends and relatives. I would keep going until I found a nice state or national park campground and hang out there. it would be far less regimented and stressful, but then what wouldn't be?
During the 07 fires I stayed at my parents place. The catch is they've almost had to evaculate during previous wildfires. With a half million evacuees hotel/motel lodging is out out the question, and any campgrounds that didn't burn were evacuated in 07.
Pray for the best and prepare for the worst.
http://en.wikipedia.org/wiki/October_2007_California_wildfires