Firefighters continue Thursday to fight a 50-acre grass fire near Cheyenne Mountain State Park, the Colorado Springs Fire Department said.

Firefighters battled the blaze through the night after it was reported Wednesday near Norad Road and Highway 115.

The department requested a bulldozer, an air tanker and a helicopter to help fight the fire amid Thursday’s red-flag conditions, when gusty winds and low relative humidity could cause the fire to spread quickly.

Due to the high winds, the helicopter and air tanker were grounded, said Captain Mike Smaldino.

Investigators arrived Thursday morning to search for what may have caused the fire, which burned in a “steep and rugged” area of the park, Smaldino said. Fifty firefighters were also on the scene, using hand tools to fight the fire, since the fire trucks were unable to get to the blaze.

Highway 115 is open, but Norad Road and the roads in the state park are closed, the department said.

No structures were threatened.