The cause of the tunnel fire was ruled “unknown.” Law enforcement and investigative units in the Southwest Region spent more than a year conducting the investigation. A tunnel fire was first reported on the afternoon of Sunday, April 17, 2022, about nine miles northwest of Flagstaff and adjacent to the Timberline/Fernwood community. Investigators said firefighters were quick to respond to the call and extinguish the fire quickly. When firefighters returned the next morning, they confirmed that all control lines were intact. They continued to check for hotspots and by 3:18 p.m. it was determined that all smoke and hotspots had been extinguished and the fire extinguished before firefighters left the area. By early Tuesday morning, two days after the initial fire broke out, a combination of 60 mph winds and warm conditions formed over the fire area. The wind prevented firefighters from containing the fast-moving fire. The fire destroyed a total of 1,335 buildings, 30 residences and 24 annexes, and expanded to over 19,000 acres before being completely extinguished on June 1. No lives were lost in this fire. Law enforcement recommends that anyone with information about the person who started the tunnel fire contact the Coconino National Forest at 928-527-3600 or the Coconino County Sheriff’s Office at 928-774-4523 (Option 1).