Nearly 400 firefighters were battling the so-called Sierra Fire, which broke out shortly before 4 p.m. west of the 15 Freeway in Sycamore Canyon.
According to the U.S. Forest Service, the blaze had scorched 200 acres by Tuesday night and threatened about 30 rural homes. There was no immediate word on containment.
Five helicopters and six air tankers were brought in to make water drops.
Voluntary evacuation orders were in place for residents along Glen Helen Road west of the 15 Freeway. The Deer Park Nudist Resort was also evacuated.
An evacuation center was established for residents at the Jesse Turner Center located at 15556 Summit Avenue in Fontana. Authorities were asking residents to take their small animals to the Devore Animal Shelter located at 19777 Shelter Way in San Bernardino.
There was no immediate word on containment.