The BLM website says that Juniper Flats has hunting restrictions...you cannot use "hunting" as justification to carry a handgun or rifle.
Hunting
This is a "shotgun only" area through a San Bernardino County ordinance. The area is closed to night shooting and recreational target shooting with rifles or hand guns. In season, you can hunt dove, quail and chuckar but season and bag limits vary.
http://www.ca.blm.gov/barstow/jflats.html