The U.S. Forest Service found in a new investigation that its own prescribed burn started a wildfire last April that nearly reached the city of Los Alamos, New Mexico. 

The Cerro Pelado Fire ripped across more than 60 square miles last spring, reaching within a few miles of the area, forcing schools to close and leading to evacuation orders.

The wildfire was traced to a burn of forest debris piles that were commissioned by the agency, with the burn becoming a holdover fire and smoldering for months, according to Southwestern Regional Forester Michiko Martin.

"Our investigation has confirmed that the Cerro Pelado Fire on the Jemez Ranger District of the Santa Fe National Forest was caused by a holdover fire from the Pino West Piles Prescribed Fire, a debris pile burn. A holdover fire is a fire that smolders undetectably. In this case, despite being covered by wet snow, this holdover fire remained dormant for considerable time with no visible sign of smoke or heat," he explained on Monday. "This investigation adds to the considerable evidence of how severely the Santa Fe National Forest was affected by extreme environmental conditions caused by historic drought in 2022."

"This fire deeply affected our communities. Escaped prescribed fires in 2022 led the Forest Service to implement a 90-day national pause on prescribed fire and review required changes to the prescribed fire program," Martin added, noting the Santa Fe National Forest has implemented these changes. 

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Fire vehicles in Jemez Mountains

A Cochiti Fire Department vehicle heads toward a plume of smoke from the Cerro Pelado Fire burning in the Jemez Mountains, April 29, 2022, in Cochiti, New Mexico. The U.S. Forest Service said on Monday, July 24, 2023, that its own prescribed burn started the 2022 wildfire that nearly burned into Los Alamos, New Mexico. (Robert Browman/The Albuquerque Journal via AP)

He also said that the Forest Service will conduct an internal declared wildfire review to learn how to conduct prescribed fires more safely and reduce the risk of them escaping, with Southwestern Region firefighters now using handheld thermal devices and drones to detect the presence of heat.

An initial probe into the origin of the fire was conducted by a wildland fire investigator from Washington state's Department of Natural Resources and pointed toward an ash pit from the earlier prescribed burn as the likely source – but did not reach a definitive conclusion. 

The news drew swift reaction from the state's top politicians, including Gov. Michelle Lujan Grisham.

"I am – again – outraged over the U.S. Forest Service’s negligence that caused this destruction. While climate change and extreme drought continue to plague the Southwest, the Forest Service must abandon their business-as-usual approach to prescribed burns and forest management in our state," she asserted. "I am relieved to hear that the Forest Service will now use technology to prevent this from occurring in the future. We will continue to hold the federal government accountable for each of the disastrous fires they caused in our state last summer."

Lujan Grisham speaks

New Mexico State Governor Michelle Lujan Grisham speaks at a rally hosted by the Democratic Party of New Mexico at Ted M. Gallegos Community Center in Albuquerque, New Mexico, on Nov. 3, 2022. (Photo by SAUL LOEB/AFP via Getty Images)

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"Today's news that yet another wildfire in NM was started by U.S. Forest Service is unacceptable. The Cerro Pelado Fire endangered NMs," Senator Ben Ray Luján said on Facebook. "This was extremely reckless. There's technology to detect these mishaps from occurring and USFS must do better to ensure this never happens again."

Senator Martin Heinrich said he was "frustrated" by the findings. 

"The warming climate is making our forests more vulnerable to catastrophic wildfires. That’s a reality that our Forest Service can and must urgently respond to when deciding when and how to do prescribed burns. We cannot catch up to this reality if it takes nearly a year to even make the findings on the Cerro Pelado Fire public," he said. 

Fire in New Mexico

The Cerro Pelado Fire, seen on May 6, 2022, from Cochiti, New Mexico, burns in the Jemez Mountains. (Robert Browman/The Albuquerque Journal via AP)

"As the Forest Service does the necessary work of updating its modeling and use of prescribed fires, it must also prioritize rebuilding the public’s trust. This will require more transparency and much more concerted and authentic engagement with New Mexicans than the Forest Service has shown up to this point," Heinrich wrote.

Last year, the Forest Service halted all prescribed burn operations for 90 days while it conducted a review of procedures and policies. 

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Forest Service Chief Randy Moore recently told New Mexico lawmakers that the agency learned managers cannot rely on past successes and must adapt to changing conditions.

The federal government has already acknowledged that it started the largest wildfire in state history, which burned more than 530 square miles.

The Associated Press contributed to this report.