Evacuation orders remained in place early Monday for thousands of people after a wildfire in mountains east of Los Angeles exploded in size and forced crews to battle flames in triple-digit heat.

The Apple Fire in Riverside County consumed more than 31 square miles (about 80 square kilometers) of dry brush and timber, according to the California Department of Forestry and Fire Protection.

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Firefighters work against the Apple Fire near Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

Evacuation orders remained in place early Monday for thousands of people after a wildfire in mountains east of Los Angeles exploded in size and forced crews to battle flames in triple-digit heat.

A firefighter watches the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

Officials allowed flames to run up the side of Mount San Gorgonio, an 11,000-foot (3,350-meter) peak, because it wasn't safe to let crews work in such steep, rugged terrain, said Lisa Cox, a spokeswoman for the U.S. Forest Service.

A brush fire burns at the Apple Fire in Banning, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Flames leapt along brushy ridge tops and came close to homes while firefighters attacked it from the ground and air.

Firefighters watch the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A huge smoke plume was visible for miles around and contributed to poor air quality.

A firefighter watches a brush fire at the Apple Fire in Banning, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches a brush fire at the Apple Fire in Banning, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews line up to work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews line up to work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

An area sits scorched by a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

An area sits scorched by a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches as a helicopter drops water onto the Apple Fire near Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches as a helicopter drops water onto the Apple Fire near Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter runs as the wind blows at the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter runs as the wind blows at the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

As of Monday morning, it was 5% contained. The cause was under investigation.

Firefighters work against the Apple Fire near Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

Firefighters work against the Apple Fire near Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

Officials allowed flames to run up the side of Mount San Gorgonio, an 11,000-foot (3,350-meter) peak, because it wasn't safe to let crews work in such steep, rugged terrain, said Lisa Cox, a spokeswoman for the U.S. Forest Service.

“We don’t want to put firefighters in a dangerous situation,” Cox told the Riverside Press-Enterprise. “It’s burning in a straight line up a mountain.”

The blaze began as two adjacent fires reported Friday evening in Cherry Valley, an unincorporated area near the city of Beaumont about 85 miles (137 kilometers) east of downtown Los Angeles.

A firefighter watches the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

Flames leapt along brushy ridge tops and came close to homes while firefighters attacked it from the ground and air.

One home and two outbuildings were destroyed, Cal Fire said. No injuries were reported.

Evacuation orders and advisories were issued for about 8,000 people in mountain, canyon and foothill neighborhoods. Campgrounds and hiking trails were closed in the San Gorgonio Wilderness area of the San Bernardino National Forest.

A brush fire burns at the Apple Fire in Banning, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

A brush fire burns at the Apple Fire in Banning, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

A huge smoke plume was visible for miles around and contributed to poor air quality.

The mercury hit 109 degrees (43 Celsius) Sunday in nearby Palm Springs. The National Weather Service said “dangerously hot conditions” were expected to continue because of high pressure over much of Southern California.

To the north, the Pond Fire in San Luis Obispo County was 10% contained Sunday after burning more than 2 square miles of (6 square kilometres) brush east of Santa Margarita. The blaze destroyed two structures but officials said it was unclear whether they were homes.

Firefighters watch the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

Firefighters watch the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches a brush fire at the Apple Fire in Banning, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches a brush fire at the Apple Fire in Banning, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews line up to work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews line up to work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

An area sits scorched by a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

An area sits scorched by a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

Hand crews work on the remaining hot spots from a brush fire at the Apple Fire in Cherry Valley, Calif., Saturday, Aug. 1, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches as a helicopter drops water onto the Apple Fire near Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter watches as a helicopter drops water onto the Apple Fire near Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter runs as the wind blows at the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)

A firefighter runs as the wind blows at the Apple Fire in Banning, Calif., Sunday, Aug. 2, 2020. (AP PhotoRingo H.W. Chiu)