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Times-News, Drew Nash, Associated Press
Bureau of Land Management firefighters work to extinguish a brush fire along U.S. Highway 26 at mile marker 188 near Dietrich, Idaho on Saturday, July 5, 2014. The fire that started Friday afternoon reached about 130 acres Saturday morning.

BOISE, Idaho — About 20 backcountry campers in the Sawtooth Wilderness had to be evacuated because of a central Idaho wildfire that several hundred firefighters are trying to snuff out before it gets too large.

More crews and equipment arrived Saturday to fight the Hell Roaring Fire burning through dead and downed trees about 12 miles south of Stanley, fire spokeswoman Barbara Bassler said.

Large air tankers are also taking part Saturday, officials said, to protect nearby cabins and trailers. There were no reports of injuries or any damage to structures.

The fire that started Friday afternoon reached about 320 acres by Saturday evening and was 60 percent contained.

Firefighters built a line on the western side of the fire and completed some burnout operations on the southeast and northeast edges, officials said. Crews planned to try to secure the northern flank Sunday.

Air tankers and helicopters worked Friday to slow the fire's growth until ground crews could arrive to start building fire lines, Bassler said.

The fire is believed to be caused by people because there was no lightning at the time, Bassler said. A fire investigator has been called to determine what happened.

Firefighters are having success on the east side, where the flames have reached grass, Bassler said. But it's not as easy in the timbered, mountainous area on the west side of the fire, she said.

"They're putting everything they can at it, with the priority the safety of the firefighters," she said. "There are lots of snags. We don't want to risk any loss of life."

Two hotshot crews from Montana are assigned to the blaze, she said.

The mountainous area is a favorite among tourists this time of year, arriving for the hiking, rafting, rock climbing, mountain biking, fishing and other activities.

The last two summers, though, businesses lost customers because of fires in the region that grew.

"We certainly understand the concern of the people up here," Bassler said. "I know people are quite nervous. We are getting resources here, and we are aggressively fighting the fire."

Idaho Highway 75, which is part of the state's scenic byway system and cuts through the middle of the high-elevation valley bracketed by mountains, is open. But the western side of Highway 75, which includes some forest roads and the Hell Roaring Trail, was closed.