By Laura Zuckerman
SALMON, Idaho (Reuters) - A 91,000-acre (38,800-hectare) wildfire in the Boise National Forest closed in from three directions on an Idaho mountain town on Monday as authorities worried about the safety of roughly 30 residents who have refused to evacuate.
The Elmore County Sheriff's Office ordered evacuations over the weekend as thick smoke from the Trinity Ridge Fire posed a health hazard and limited visibility on the single road to Featherville, a popular summertime resort at the foot of the Trinity Mountains on the South Fork Boise River.
"It puts everyone in higher danger. Firefighters will have to worry about the safety of people who are left behind instead of fighting the fire and saving homes," U.S. fire information officer Mary Christensen said.
Fire crews prepared to defend hundreds of homes in Featherville, where second homes and rental cabins cause the summer population to swell to roughly 1,000, as well as structures in the nearby community of Pine.
"We hope those residents will reconsider and get out of there," Christensen said.
Weather forecasters predicted a blanket of thick smoke that has lowered temperatures and slowed the fire's march to Featherville would lift.
The fire has burned over 90,000 acres of sagebrush and timber in south-central Idaho since it was ignited on August 3 by an off-road vehicle that caught fire, authorities said. It was only 5 percent contained on Monday.
Flames also threatened a critical stretch of the North Fork Boise River drainage where fire managers had hoped to cordon off the blaze to prevent its spread eastward toward the historic mining town of Idaho City.
Crews sought to construct fire lines by hand in the steep, rugged terrain ridging the river, Christensen said.
So far this season, wildfires have consumed roughly 6.9 million acres (2.8 million hectares) across the United States, over 1.5 million acres more than the 10-year average for this time of year, according to the National Interagency Fire Center in Boise.
The Idaho fire was one of dozens burning across 10 parched western states, with Nevada, Idaho, and California each seeing hundreds of thousands of acres charred.
In California, a fire has burned across 15,000 acres in the north-central part of the state, destroying seven houses and threatening 3,500 others. Dubbed the Ponderosa fire, it was only 5 percent contained as of Monday afternoon.
In the northeast corner of the state, a fire burned near a major natural gas line and transfer station, as well as power lines that serve Reno, across the border in Nevada, according to fire officials.
That blaze, named the Rush fire, had burned through more than 270,000 acres and was 50 percent contained on Monday.
(Writing and additional reporting by Mary Slosson; Editing by Jim Loney)