HIGHLAND, California — Out-of-control wildfires in the foothills of a national forest east of Los Angeles and in a recreation area south of Reno, Nevada, threatened buildings and forced hundreds of residents to flee a days-long heat wave with temperatures above 90 degrees.

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. By Monday morning, the blaze had charred about 32 square miles (83 square kilometers) of grass and chaparral and blanketed the area in a thick cloud of dark smoke.

The storm remained out of control, threatening more than 36,000 structures, including single-family homes, multi-family dwellings 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). The blaze started in Davis Creek Regional Park in the Washoe Valley and burned through heavy timber and brush, fire officials said. That fire, too, was not contained.

A state of emergency that Gov. Joe Lombardo declared Sunday for Washoe County said about 20,000 people had been evacuated from neighborhoods, businesses, parks and campgrounds. Part of south Reno remained under evacuation orders Monday, fire officials said, and some homes, businesses and traffic lights in the area were without power.

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

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

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

“It came down to what’s worse, being stuck or being in a shelter?” King said Sunday outside an evacuation center. “As circumstances changed, I had to make a quick decision, just a couple of packages and everything fit in a shopping cart.”

Joseph Escobedo said his family has lived in Angelus Oaks for about three years and has never evacuated because of wildfires. His family, which includes three young children, was among the few who had not left by Sunday afternoon.

“It’s pretty scary to lose your home and everything that we’ve worked so hard for,” Escobedo said as his family packed up supplies to leave. “It’s hard to leave and not know if you can come back.”

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

Smoke already hung in downtown San Bernardino, where Joe Franco, an employee at Noah’s Restaurant, said his friends in surrounding evacuation zones were preparing to leave at a moment’s notice.

“They’re just kind of holding on and getting their stuff ready to move,” Franco said. “They’re usually here, but today a lot of people aren’t coming.”

Redlands Unified School District canceled classes for about 20,000 students on Monday, and Gov. Gavin Newsom declared 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. About 4,000 people were forced to evacuate by the Boyles Fire, which was about 10% contained Monday morning.

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