(CNN) -- A helicopter bombarded a forest with ping-pong balls filled with flamable fuel in an effort to contain a wildfire north of Bend, Oregon, a fire official said.
The Rooster Rock Fire in Deschutes National Forest-administered lands has charred 6,130 acres since it was first reported on Monday, according to a statement from the Central Oregon Interagency Dispatch Center.
Cooler temperatures and lighter winds Thursday allowed firefighters to reach 40 percent containment and secure their fire lines by Friday, the statement said.
"This gave firefighters an opportunity to burn out a large island of unburned fuels on the west flank that if allowed to burn during the hotter part of the day, could have potentially thrown embers outside the established control lines," it said.
The fuel-filled ping-pong balls were dropped from the air to ignite the island "in a systematic fashion," it said.
No buildings are immediately threatened by the fire, but the popular recreation area has been closed to visitors, it said.
The cause of the fire is under investigation.