The Martin Canyon Fire burning east of Bellevue in Blaine County has grown to roughly 3,500 acres and is now 25% contained.
Fire officials now believe the fire was sparked Sunday afternoon by someone target shooting in the canyon.
Authorities have not yet found the person responsible, but say they could be held liable for the damage and firefighting costs.
"It's hot. It's dry. Its going to get hotter through the month of August and the rest of July," Fire Information Officer Ryan Berlin said. "Just be heads up on your surroundings. If your out target shooting try to go to some designated areas that is made for target shooting and not on public land."
Crews conducted back burning operations Monday to eliminate fuels ahead of the fire.
Fire crews plan to remain on scene for several days, hoping for full containment Wednesday.
Crews are fighting flames from the ground and the air and have already received reports of people flying drones nearby. People are urged to stay away from the area.