The terrain-driven blazes, reported about 2:20 a.m., were approximately 1/2 mile apart and had burned 5 and 10 acres, respectively, by 6:30 a.m., according to the Los Angeles County Fire Department. Containment was 70 percent after multiple water drops at the scene.
No injuries were reported, nor were any homes threatened, said Battalion Chief Mike Blawn of the Orange County Fire Authority.
Arson investigators from the Los Angeles County Sheriff's Department responded to the location, where a witness reported seeing a suspicious man "with a white scarf around his face wearing blue jeans and driving a black sedan." The witness reported seeing the man setting the fires.
When California Highway Patrol officers initially arrived at the scene, six separate fires were burning. The flames then coalesced into two blazes -- one in L.A. County proper, the other in Orange County.
The blaze initially prompted the closure of all northbound lanes on the 57 Freeway, officials said. The northbound 57 was closed for more than five hours at Brea Canyon Road. The carpool lane and the fast lane were reopened about 7:45 a.m. The southbound side was not affected.
Detectives asked anyone with information about the incident is asked to call sheriff's Detective Greene at (323) 881-7500.