Massive California fire threatening 4,700 structures as new blaze ignites in Colorado

As one of the largest wildfires in California history, the Park Fire in Northern California, continued to rage Monday, another large blaze in the Western U.S. ignited in Northern Colorado prompting evacuations.

The Park Fire in Northern California was racing across four counties Monday and threatening more than 4,200 structures as thousands of firefighters struggled to increase containment lines, officials said.

While firefighters battled the Park Fire Monday, the Alexander Mountain Fire ignited near Roosevelt National Park in Larimer County, Colorado, north of Boulder. The fire was initially estimated to be burning about 247 acres at around 12:45 p.m. local time Monday, but within two hours had quickly spread to 800 acres, according to the National Park Service.

The Larimer County Sheriff's Office issued orders for residents in Alexander Mountain and Palisade Mountain areas to "evacuate immediately" as local fire crews and firefighting aircraft raced to battle the blaze.

The Park Fire is now the 6th largest in state history

Meanwhile, the Park Fire, which California authorities said was deliberately ignited Wednesday afternoon, had spread to 370,237 acres by Monday afternoon, or more than 560 square miles, through Butte, Plumas, Shasta and Tehama counties, according to the California Department of Forestry and Fire Protection (CAL FIRE). Containment on the fire remains at 12%, officials said.

"That's actually a good thing," Rick Carhart, a CAL FIRE spokesperson, told ABC News on Monday of the amount of containment firefighters have achieved. "We had no containment on the fire until yesterday morning, so the last day and a half, we've been able to make really good progress."

The Park Fire is the largest fire burning in the state and the nation right now, surpassing the 288,690-acre Durkee Fire in eastern Oregon, which was sparked on July 17 by a lightning strike and was 49% contained as of Sunday evening, according to the Oregon State Fire Marshal's Office.

The Park Fire is now the sixth largest fire recorded in California history, officials said. It comes as the state battles 22 other fires, including some as small as 12 acres as of Monday.

More than 100 structures have been confirmed destroyed, and at least five others damaged, according to CAL FIRE. There have been no reports of deaths or people unaccounted for, officials said.

The Butte County Sheriff's Office lifted some evacuation orders on Sunday. But evacuees like Nalley Orozco told ABC News they had nothing to return to but charred rubble.

Orozco, of the Butte County town Cohasset, was one of more than 3,800 people forced to evacuate as the Park Fire consumed her home and reptile-breeding business Killer Clutches.

"We left everything behind, all personal belongings, all of the enclosures, all the supplies," Orozco told ABC News, adding that she was able to save all of her animals but lost her home and business.

The rapid spread of the fire is being fueled by an abundance of vegetation and one of the hottest and driest summers on record in the area, officials said.

"It's been very, very dry. The relative humidity level has been in the low teens to sometimes down in the single digits. So fuel moisture is almost nonexistent. Everything is ready to burn here," Carhart told ABC News.

Temperatures in the area, which have been in the triple digits, cooled slightly to a high of 92 degrees on Sunday in the Chico area, according to the National Weather Service. Winds also died down in the area, but gusts of up to 20 mph are expected on Monday.

In an updated statement Sunday evening, CAL FIRE said that the cooler night and morning temperatures of about 70 degrees moderated the fire behavior, "allowing fire crews the opportunity to actively combat the fire outside of the National Forest lands."

"This proactive approach aims to safeguard the communities and ecological and cultural resources that may be at risk from the fire," CAL FIRE said in its statement.

The high temperature on Monday in the fire zone is forecast to be 94 degrees, according to the National Weather Service. By the end of this week, temperatures are forecast to spike back into the 100s, according to the weather service.

California Gov. Gavin Newsom declared a state of emergency for Butte and Tehama counties due to the Park Fire, as well as Plumas County, where the Gold Complex Fire, which started on July 22, has burned more than 3,000 acres and was 50% contained on Monday.

Ronnie Dean Stout II, 42, was arrested on suspicion of arson in the Park Fire after he allegedly pushed a burning car into a gully in Bidwell Park, near Chico, according to Butte County District Attorney Mike Ramsey. Stout, who is being held without bail in the Butte County Jail, is scheduled to be arraigned on Monday afternoon.

"I don't know if I'd say I'm angry, but frustration and unnecessary, yes," Chico-area rancher John Russell told ABC News of learning the fire was deliberately set.

Russell said the fire burned up to this property line but was stopped by firefighters who cut a fire line around his land with a bulldozer to save his barn and cattle.

"I know I'm being recorded, so I won't say obviously, I'll put it tactfully... Our cattle survived. We can go on. We can fix the rest. But truly, the real damage and sadness and anger would come from the people who have lost everything," Russell said.

There are more than 4,700 personnel, 16 helicopters and 337 fire engines assigned just to the Park Fire, officials said.

"Numerous firefighting air tankers from throughout the state are flying fire suppression missions as conditions allow," according to CAL FIRE.

A fire burning near the Sequoia National Park, the 2024 SQF Lightning Complex Fire in Tulare and Kern counties in Central California, is the second largest blaze burning in the state, having consumed 82,699 acres since starting on July 13, according to CAL FIRE. The blaze was 33% contained on Monday.

The heavy smoke from fires in Northern California and Oregon is spreading across several states, including Nevada, Idaho, Utah, Wyoming and Montana. By Monday afternoon, some of the heavy smoke is expected to reach as far as the Dakotas and Nebraska.

This fire season in California began in earnest in early July and hasn't slowed down since, officials said. So far this year, 4,574 fires have erupted in the state and have burned a combined 726,667 acres, an increase of 2,744% from this time last year, according to CAL FIRE.

ABC News' Mola Lenghi and Jaclyn Lee contributed to this report.