An out-of-control wildfire in the San Bernardino National Forest tore through 18,000 acres of brush and timber Saturday, forcing evacuations in a pair of mountain communities.

The entire resort community of Green Valley Lake and the Fawnskin area near Big Bear Dam were under a mandatory evacuation order. About 5,000 people were affected, said Jim Wilkins of the San Bernardino County Fire Department.

"It's just been running and gunning all day long, eating up ground," Wilkins said. "It's a very aggressive fire burning through fuels that haven't been burned in 50 to 75 years."

Winds of about 20 miles an hour and humidity of just 10 percent were helping the blaze grow and it crept within a half-mile of homes in Fawnskin, Wilkins said.

Evacuation centers were set up at Big Bear High School in Sugarloaf for Fawnskin residents and at Rim of the World High School for Green Valley Lake.

The fire was reported around 1:30 p.m. Friday, and it was 5 percent contained Saturday afternoon.

Voluntary evacuations were called for Lucerne Valley south of the Pitzer Buttes area, authorities said.

Highway 18 was closed between Arrowbear and Big Bear Dam, authorities said. The downhill lanes are open. Highway 38 was shut from Big Bear Lake to Discovery Center.

Fire officials also evacuated the Camp Whittle, Hannah Flats, Big Pine Flats and Ironwood campgrounds.

About 600 firefighters were aided by water drops from helicopters, fixed-wing aircraft and a DC-10 capable of dropping 24,000 gallons at a time as they battled the blaze, which was burning in steep terrain.

The blaze formed a column of smoke so large that its effects were being felt as far away as Las Vegas, Smith said.

The fire, which is being called the Butler 2 fire, was burning near the site of the first Butler fire, an 85-acre blaze that was sparked by lightning on Sept. 1 in an area west of the lake.

Its cause was under investigation.

Meanwhile in San Diego County, several dozen homes in Whispering Pines, a subdivision of the historic town of Julian, were evacuated after a 500-acre wildfire erupted northeast of town shortly after 1:30 p.m., county sheriff's officials said.

Also on Saturday, crews were mopping up a fire that charred 2,170 acres in a remote mountainous area east of San Diego. The blaze in the Cleveland National Forest was 95 percent contained, California Department of Forestry and Fire Protection spokeswoman Audrey Hagen said. Full containment was expected by the evening.

The fire was started by an illegal campfire Wednesday afternoon and spread rapidly due to drought conditions. It remained about two miles from Pine Valley, a hamlet 40 miles east of San Diego and a few miles north of the Mexican border.

One firefighter suffered burns on the ear and hand and another suffered heat-related injuries.