The Radford Fire was first spotted around 2 p.m. in an area between the ski resorts Snow Summit and Bear Mountain.
It has burned 200 acres in the San Bernardino National Forest and was 0% contained as of 7 p.m. Firefighters were attacking the flames from the ground and air.
Four air tankers and four helicopters are making drops, with at least 140 personnel assigned.
The San Bernardino County Sheriff's Department has ordered evacuations for Glass Road to South Fork River Road.
Caltrans says State Route 38 is closed in both directions from Mill Creek Road to Lakewood Road.
The area being evacuated is in the Seven Oaks community.
The cause of the fire was not immediately known.