San Bernadino county thinks they have the authority to limit rifle shooting on federal property. Since the federal courts haven't broke that one off in the county shoot at your own risk. The BLM rangers in the area told me that they don't enforce city or county laws on federal property.
The BLM rules are pretty wide. Here's the Barstow area web page:
Target shooting is allowed on land managed by the Bureau of Land Management (BLM). The legal target shooting area is the area north, northwest, or northeast of Barstow, taking into consideration any private land, posted signs, and other rules and regulations that would apply. It is the responsibility of the shooter to know the laws for the area where they are shooting.
http://www.blm.gov/ca/st/en/fo/barstow/recshoot.html
Do not shoot within 150 yards of any man-made object, camp, domestic livestock, or occupied dwelling. Don't trash the desert as the rangers will go to town on you.