SANTA FE, N.M. — Two fires that merged to create the largest wildfire in New Mexico history have both been traced to planned burns set by U.S. forest managers as preventative measures, federal investigators announced Friday.

The findings shift responsibility more squarely toward the U.S. Forest Service for initiating a natural disaster that has destroyed at least 330 homes as flames raged through nearly 500 square miles of high-altitude pine forests and meadows. The wildfire also has displaced thousands of residents from rural villages with Spanish-colonial roots and high poverty rates, while unleashing untold environmental damage.

Roughly 3,000 firefighters, along with water-dropping planes and helicopters, continue to fight the blaze as it approaches mountain resorts and Native American communities. Firefighting costs already surpass $132 million, climbing by $5 million a day.

Fire and law enforcement officials offered a cautious but hopeful Friday night status report, with fire behavior analyst Stewart Turner noting they need to watch the so-called “red flag” conditions — warm, dry weather with high winds — starting Saturday.

“The weather is a big concern for us,” Turner acknowledged, saying even an errant pine cone rolling down a slope and crossing a control line could spread flames. “Red flag warning is a big message for tomorrow.”

He said dry conditions are expected through Tuesday, but some moisture and even thunderstorms are possible starting Wednesday.

Congresswoman Teresa Leger Fernández described a rising sense of outrage as the fire triggers new evacuations of families and livestock. Fear of flames is giving way to concern about erosion and mudslides in places were superheated fire penetrates soil and roots.

“The destruction these two fires caused is immeasurable and will be felt for generations,” said Leger Fernández, sponsor of a bill that would reimburse residents and businesses routed by the fire.

The Forest Service has not yet released detailed planning documents for the original planned burns that might indicate whether fire protocols were followed.

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What is a prescribed burn?

Scientist and forest managers are racing to develop new tools to forecast the behavior of planned fires amid climate change and an enduring drought in the American West. The intentionally set blazes, known as prescribed burns, are aimed at limiting the accumulation of timber and underbrush that, if left unattended, can fuel extremely hot and destructive wildfires.