A slow-moving brush fire burned 55 acres in Irvine Regional Park on Sunday, but no structures were threatened and there were no injuries reported, authorities said.
Full containment was expected by midnight, said Capt. Stephen Miller, spokesman for the Orange County Fire Authority. About 100 firefighters were working on the blaze.
"The terrain is steep, and we've had to do most of the work from the ground," Miller said. "It was even hard for the helicopters to get in there."
The fire began about 12:30 p.m. in the park, near the Holy Sepulcher Cemetery in Orange. Winds of about 3 mph pushed the fire slowly east along a hillside and away from Santiago Canyon Road and homes, Miller said.
The cause of the fire was unknown, and arson investigators were on the scene, Miller said. Rangers closed the park to hikers and bikers at 3:30 p.m. as a precaution.