The fire, dubbed the Panorama Fire, broke out just before 2 p.m.
Firefighters from the U.S. Forest Service, California Fire, San Bernardino county and city departments were battling the blaze. At least 23 fire engines were on scene, along with helicopters .
Voluntary evacuations were lifted for residents in Waterman Canyon. By 11 p.m., the fire was 30 percent contained, according to the Forest Service website.
Highway 18 was closed to all traffic from State Route 138 to 40th Street in San Bernardino. Highways 330 or 138 through the Cajon Pass were recommended as alternate routes. Old Waterman Canyon Road was reopened by 6 p.m.
As of 5 p.m., some structures in the area were being protected, though none were in immediate danger. A communications site was in the path of the fire, but the blaze turned in a different direction.
At least three firefighter sustained heat-related injuries, officials said."Our big concern is that we're going into triple-digit weather and there is a possibility of dry lightning, perhaps Wednesday, Thursday," said John Miller, a Forest Service spokesman. "We're going into a high-state of readiness, being prepared for what Mother Nature might throw at us."
The cause of the fire was under investigation. A small area believed to be where the fire originated was taped off and was being considered a crime scene.