HIGHLAND, Calif. (AP) — Out-of-control wildfires in the foothills of a national forest east of Los Angeles and in a recreational area south of Reno, Nevada, threatened buildings and forced hundreds of residents to flee amid a days-long heat wave of triple-digit temperatures.

In California, the so-called Line Fire was burning along the edge of the San Bernardino National Forest, about 65 miles (105 kilometers) east of Los Angeles. As of Monday morning, the blaze had charred about 32 square miles (83 square kilometers) of grass and chaparral and blanketed the area with a thick cloud of dark smoke.

It remained uncontained, threatening more than 36,000 structures, including single and multi-family homes and commercial buildings, the U.S. Forest Service said.

About 20 miles outside Reno, Nevada, the Davis Fire, which started Sunday afternoon, has grown to about 10 square miles (26 square kilometers). It originated in the Davis Creek Regional Park in the Washoe Valley and was burning in heavy timber and brush, firefighters said. It, too, was not contained.

An emergency declaration issued for Washoe County by Gov. Joe Lombardo on Sunday said about 20,000 people were evacuated from neighborhoods, businesses, parks and campgrounds. Some of south Reno remained under the evacuation notice on Monday, firefighters said, and some homes, businesses and traffic signals in the area were without power.

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The California fire burned so hot Saturday that it created its own thunderstorm-like weather systems of pyroculumus clouds, which can create more challenging conditions such as gusty winds and lightning strikes, according to the National Weather Service. Firefighters worked in steep terrain in temperatures above 100 degrees (38 Celsius), limiting their ability to control the blaze, officials said. State firefighters said three firefighters had been injured.

Evacuations were ordered Saturday evening for Running Springs, Arrowbear Lake, areas east of Highway 330 and other regions.

Running Springs resident Steven Michael King said he had planned to stay to fight the fire and help his neighbors until Sunday morning, when the fire escalated. He had prepped his house to prevent fire damage but decided to leave out of fear smoke could keep him from finding a way out later.

“It came down to, which is worse, being trapped or being in a shelter?” King said outside an evacuation center Sunday. “When conditions changed, I had to make a quick decision, just a couple of packs and it all fits in a shopping cart.”

Joseph Escobedo said his family has lived in Angelus Oaks for about three years and has never had to evacuate for wildfire. His family, with three young children, was among the remaining few who hadn’t left as of Sunday afternoon.

“It’s kind of frightening with the possibility of losing your home and losing everything we worked really hard for,” Escobedo said as his family packed up the essentials to leave. ”It’s hard to leave and not be sure if you’re gonna be able to come back.”

The affected area is near small mountain towns in the San Bernardino National Forest where Southern California residents ski in the winter and mountain bike in the summer. Running Springs is on the route to the popular ski resort town of Big Bear.

Smoke already blanketed downtown San Bernardino, where Joe Franco, a worker at Noah’s Restaurant, said his friends in the surrounding evacuation zones were gearing up to leave at a moment’s notice.

“They’re just kind of hanging on tight and getting their stuff ready to move,” Franco said. ”Normally they’re here, but a lot of people are not coming today.”

Redlands Unified School District cancelled Monday classes for roughly 20,000 students, and Gov. Gavin Newsom proclaimed a state of emergency for San Bernardino County.

Meanwhile, a small vegetation fire, less than a square mile (2.6 square kilometers), burned at least 30 homes and commercial buildings and destroyed 40 to 50 vehicles Sunday afternoon in Clearlake City, 110 miles (117 kilometers) north of San Francisco, officials said. Roughly 4,000 people were forced to evacuate by the Boyles Fire, which was about 10% contained Monday morning.

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Associated Press reporter Kathy McCormack in New Hampshire contributed to this story.