A controlled burn in the thick brush of the San Bernardino National Forest jumped across a road and spread out of control over 600 acres Thursday.
Two abandoned structures burned, but no homes were in immediate danger. No injuries were reported.
U.S. Forest Service crews had been using helicopters to burn out vegetation in a 5,000-acre area for more than a week when the fire spread into an uncontrolled area at 1 p.m., spokeswoman Ruth Wenstrom said.
The fire broke out along the northeast corner of the controlled burn area and spread north toward campgrounds and a lookout tower.