There is also Johnson Valley. It is approx 50 Miles from Barstow, and it is huge. It is free! I have never ridden the whole area just a little of it. Close by there is SLASH X witch is also a nice place to ride and is also free. There is even a cafe out there by SLASH X never been in there but they say it is a good place to pick up some food and beer.
The only bad thing about Johnson Valley is that the government is trying to close the place down to make a live firing rang for the military.
http://www.blm.gov/ca/st/en/fo/barstow/stoddard.html
http://www.blm.gov/ca/st/en/fo/barstow/johnson.html
Hope this helps some of the So Cal. riders!