SALMON, Idaho (Reuters) - Sixteen firefighters in Idaho held their own on Tuesday against a fierce wildfire that forced dozens of their colleagues to retreat as it raged along the Montana border, devouring 18,000 acres of rugged forest.
The 16 crew members hunkered down around a small ranch in the Frank Church River of No Return Wilderness after 40 other firefighters were pulled back on Monday as the blaze grew in size and intensity, the U.S. Forest Service said.
Agency officials said the 16 firefighters were not trapped and could be reached by helicopter airlift if necessary.
Jesse Bender, a spokeswoman for the Salmon-Challis National Forest, said the crew was left behind to defend ranch structures by clearing dense vegetation that could serve as potential fuel and laying hose lines for sprinkler grids.
The blaze grew from two lightning-caused fires that erupted August 10 and 14 in east-central Idaho, about 35 miles northwest of Salmon, then merged on Monday after flames spread into the Bitterroot National Forest in western Montana.
A tall mushroom cloud from the blaze, churning through pine, spruce and fir forest that has not burned for a century, was visible for over 100 miles.
The combined conflagration, dubbed the Saddle Complex fire, rapidly grew from about 700 acres early on Monday to 18,275 acres as of Tuesday morning, ranking it as the largest active wildfire in the nation, according to the National Interagency Fire Center in Boise.
The 2011 fire season was shaping up to be the worst in five years in terms of acreage burned in the year to date, with more than 6.5 million acres charred by wild land blazes.
At last count, 26 large wildfires were burning in 14 states across the country, from Virginia to Washington, the agency said, including seven in Montana alone.
About half of the burned acreage from the Saddle Complex lies in Idaho, the other half in Montana, where fire crews were girding to protect homes west of the towns of Darby and Sula.
No injuries have been reported, but the blaze has burned through a popular campground and hot springs northwest of Salmon, Idaho, and threatened a lookout station in the area.
FIRE THREATENS HOMES IN MONTANA
About 75 miles north of the Saddle Complex, a smaller blaze scorched about 2,000 acres of forest and logged timberlands, threatening dozens of homes near Missoula, Montana, and prompting some residents to stand by for evacuations.
"We've got stuff packed -- clothes, things that matter -- and we're ready to go with our two dogs and cats if firefighters say we have to go," said Jacques Damon.
He sat with his brother and a friend in lawn chairs at their home in the Missoula suburb of West Riverside, watching firefighters battle flames that came within 150 feet of their neighborhood.
Ali Lovell, who lives two doors away, said flames advanced to within 10 feet of her home before dawn on Tuesday.
"It was right there and I was thinking we needed to get stuff packed up," Lovell said. "But the fire ran out of fuel because my husband had cleared the area pretty well for summer."
Firefighters said the blaze was believed to have been triggered by two careless teenagers with cigarettes, although the cause remained under investigation.
About 100 miles to the south of the Saddle blaze, firefighters managed to contain a separate fire by Monday night that had burned over 100 acres west of a nuclear reactor complex at the Idaho National Laboratory.
That fire started from a vehicle with a blown tire dragging the metal rim along the pavement of a state highway near the laboratory. Officials said there was no known radiation threat to the public.
(Additional reporting by Lori Grannis in Missoula; Writing by Steve Gorman; Editing by Cynthia Johnston)