Weeks after the final flames subsided, fire investigators have determined the likely cause and location of the Museum Fire.
According to a United States Department of Agriculture (USDA) news release Thursday morning, the wildfire originated during restoration work by the Flagstaff Watershed Protection Project.
"[The Museum Fire] was likely caused by an excavator striking a rock during operations," the press release stated. "The resulting spark created a heat source that hibernated until warm, dry and windy conditions arrived that caused the heat source to grow."
According to the release, fire prevention rules mandate that equipment operators complete a hour-long fire watch before vacating the area. In the case of the Museum Fire, the operator did complete a fire safety watch. The news release also reports the first signs of fire were seen 14 hours after the conclusion of equipment usage. During this time, it is likely that sparks and heat were embedded within the ground, eventually starting the Museum Fire.
"Deep layers of forest fuels and roots can hold heat for long periods of time, burning and smoldering underground for days, weeks or months without any sign of a fire," the release stated. "They can surface at a later time when temperatures become warmer and the weather becomes windier, causing a wildfire."
According to the Flagstaff Watershed Protection Project website, the 2012 partnership between the Coconino National Forest, Flagstaff and Arizona are designed to reduce the risk of wildfires. The project, which has a $10 million bond, coordinates prescribed burns and loggings in the Flagstaff area, among other management tactics.
The USDA news release states that the Museum Fire was not caused by negligence or a failure to comply with inspection procedures. Proper forest restoration work still has various dangers and consequences.
"It's unfortunate that the Museum Fire started as a result of ongoing restoration work designed to reduce the risk of uncharacteristic wildfire and improve forest health," Coconino National Forest Supervisor Laura Jo West stated in the news release.
According to the news release, post-fire analysis shows 50% of the Museum Fire burned at low severity, 38% at moderate severity and 12% at high severity. The fire burned 1,961 acres of the Coconino National Forest.
Flagstaff Mayor Coral Evans also spoke about the importance of the Flagstaff Watershed Protection Project, noting the valuable restoration work it has helped to orchestrate over the years.
"While the cause of the fire was unfortunate, it does not take away from the significant mitigating impact the treatment work had on the fire and subsequently the forest and our watershed," Mayor Evans stated in the news release.
The results detailed in the USDA news release are preliminary, and more information will be provided as available.