Investigators are trying to determine what sparked a grass fire south of Sun Valley early Thursday morning.

Cheyenne Fire Rescue spokesman Scott Smith says crews were called to the area shortly after 5 a.m. and had the fire out at 9 a.m.

"When firefighters arrived on scene the fire's flames were six feet to eight feet high," said Smith. "It was moving to the east and had consumed about five acres of grass."

Smith says some structures along Savannah Drive were threatened when the wind changed the path of the fire to the northwest, but no structures were damaged.

Four agencies worked to extinguish the blaze, which burned approximately 19.4 acres.