YAKIMA, Wash. — A brush fire that blackened 10 acres along the 5900 block of Cowiche Canyon Road is being investigated as suspicious, officials say.

Naches Heights firefighters had to protect heavy equipment parked above the fire on Naches Heights Road, according to a news release issued Wednesday by the Yakima Fire Department.

Firefighters allowed the fire to burn out in place because of the steepness of the terrain. Winds were also low.

Yakima County fire marshals are investigating the circumstances.

About 40 firefighters from Yakima, Naches Heights, West Valley, East Valley, Gleed, Union Gap, Highland, Selah and the Yakima Training Center spent three hours extinguishing the fire.