A Montana wildfire quadrupled in size to more than 20,000 acres in one day and burned down 10 homes and three bridges as it swept out of timberland outside the state capital at Helena, then briefly threatened another 100 homes before the winds shifted. (Utah fires story on G28.)

It was the most dangerous wildfire burning in the West, where thousands of square miles of land have been blackened in a fire season worsened by the drought.Other major conflagrations were burning in Yellowstone Park in Wyoming, where flames flared up again Thursday and forced the closing of a third campground. About 2,200 firefighters from as far away as Texas were manning the lines.

The wind shifted Thursday on the Montana blaze, burning about 10 miles southeast of Helena, blowing flames away from 75 to 100 threatened houses, but they posed new dangers to scattered ranches along the fire's east side.

"Things have laid down well on the side that burned so vigorously last evening," said Bob Krepps of the Helena Interagency Dispatch Center. "We're feeling a little more comfortable than we were last night, but in other ways, we're not as comfortable."

Cooler weather helped hold the blaze in check today but winds of 15 mph to 20 mph were expected to fan its flames later. The fire covered between 22,000 and 25,000 acres.

"The fire seems to be laying down. There's an inversion over the fire and it's not moving in any direction," said Art Howell, information officer for the U.S. Forest Service. "There's a lot of smoke over the fire."

"Our plan of attack is to continue to build lines down the east side of the fire and to maintain the lines already built," Howell said.

Starting in a roadless Forest Service management area, the fire roared out of control in the shifting winds Thursday, growing quickly from 5,000 acres to what Krepps said was well over 20,000 acres.

Krepps said the 10 structures burned by the fire included four permanent residences. The others were summer or weekend homes. Three bridges also were caught in the fire.

On Wednesday, about 20 full-time residents were evacuated from their homes in the McClelland Creek drainage. An undetermined number of others left voluntarily as the fire moved into more heavily populated areas near Montana City.

At least 1,500 firefighters from the Forest Service, Bureau of Land Management, the state of Montana and local fire districts battled the fire, aided by aerial retardant drops and a fleet of fire engines.