The fire was reported shortly before 2 p.m. in the area of Oak Glen Road. The blaze eventually grew to about 35 acres and was moving at a moderate rate of speed, according to fire officials.
Cal Fire San Bernardino tweeted out that there were six hand crews, four air tankers and three helicopters aiding in the firefight. It was unclear if the structures threatened were homes.
Oak Glen Road was closed between Wildwood Canyon and Pine Bench.
The cause of the blaze was unknown.