RENO, Nev. — Triple-digit heat across much of the U.S. West hampered crews battling scores of wildfires Thursday, including one threatening dozens of structures in Montana and another that temporarily shut down the main travel route to the Burning Man counterculture festival in the Nevada desert.

Thousands of people have been driven from their homes amid hot weather in Oregon, Montana and California, where a blaze burned 10 homes and threatened 500 more near a hard-hit community and another kept a popular road to Yosemite National Park closed.

A wind-driven wildfire ripped through parched forest and grasslands in southeastern Montana on Thursday, threatening 35 homes and structures and forcing the evacuation of an undetermined number of residents scattered in the area.

The fire that started in Custer National Forest about 35 miles (56 kilometers) northwest of Broadus on Wednesday burned at least 47 square miles (121 square kilometers) in a single day. Another fire about 60 miles (96 kilometers) south of the Canadian border destroyed five cabins and five other structures and threatened 130 more buildings Thursday in the mountains south of Havre.

In Nevada, more than 70,000 people were expected at the Burning Man art and music celebration in the Black Rock Desert by the time it culminates Saturday night with the burning of a towering effigy, and the vast majority got there by a state highway that was closed for several hours because of the fire.

“The traffic is moving, but you had a lot of congestion built up so it’s very slow going,” Nevada Highway Patrol Trooper Dan Gordon said of State Route 447.

The lightning-sparked fire has burned about 80 square miles (207 kilometers) and is about 40 miles (64 kilometers) south of the festival. Seven ranches were threatened, but there was no threat to the festival and there were no reports of injuries.

“It’s not close to Burning Man at this time,” Interagency Fire spokesman John Gaffney said. “There’s a considerable distance between the fire and the festival. At this point, the goal is to keep the road open as much as we can.”

Interagency Fire spokesman John Gaffney said the heat, expected to hit 100 degrees (37 Celsius) again on Friday, was one of the biggest concerns for crews fighting the flames by the air and ground. It’s chewing through brush that’s 1 to 2 feet high, he said, and high temperatures were expected through the weekend.

Burning Man spokesman Jim Graham said in an email that the local festival airstrip, which is built each year, is open and the celebration was continuing as scheduled.

“At the moment there is no impact,” he said.

Other fires in Nevada closed a 65-mile stretch of highway just south of the state line with California and burned a remote part of a vast former nuclear proving ground.

Nevada National Security Site spokeswoman Tracy Bower said the lightning-sparked fire covered almost 4 square miles (10 square kilometers) but wasn’t considered a threat to people or buildings.

More than 1,000 nuclear detonations occurred at the former Nevada Test Site north of Las Vegas from 1951 to 1992. It now hosts non-nuclear experiments and safety training.

Elsewhere, thousands of people have fled about two dozen fires in Oregon alone.

In Northern California, Gov. Jerry Brown has declared a state of emergency for a rural wildfire that has forced the evacuation of 2,500 homes.

Brown’s declaration for the fire in Trinity County on Thursday night says the blaze has destroyed multiple homes, but neither he nor the U.S. Forest Service have said how many.

The fire that started Wednesday night for unknown reasons is burning out of control in extreme heat and very dry conditions.

Elsewhere in California, more than 1,000 firefighters were able to slow the growth of a nearly 5-square-mile wildfire (13-square-kilometer) overnight near the town of Oroville, an area already hard-hit by fire and a massive evacuation earlier this year caused by damage to sections of the nation’s tallest dam.

It was partially contained, but about 500 homes remained in its path.

Fires also burned near Yosemite National Park, evacuating nearby towns and keeping a popular road into the park shut down. About 58 homes near the park were destroyed earlier this summer.

Air quality from wildfire smoke is a problem in Montana and Oregon, where athletic events — from kayaking and half-marathons to high school football games — have been postponed in the outdoors-loving state.

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Associated Press writers Olga Rodriguez in San Francisco, Matt Volz in Helena, Montana, Steven DuBois in Portland, Oregon, and Ken Ritter in Las Vegas contributed to this report.