Firefighters reported making progress on the 140,000-acre blaze, but officials said it continued to expand, the Los Angeles Times reported. Mike Dietrich of the U.S. Forest Service said pushing the fire back would be the operation's "No. 1 priority in the next few days," the Los Angeles Times reported.
The eastern flank was burning in the San Gabriel Wilderness Area near Devil's Canyon, U.S. Forest Service spokesman Nathan Judy said. To the west, officials were worried about the fire encroaching on Little Tujunga Canyon, made difficult to reach because of its rugged terrain.
Officials said the cause of the fire was unknown. Authorities Wednesday established a "crime scene" around the area where the fire began, the Times said.
"Right now, there is no definitive cause," said Steve Whitmore of the Los Angeles County Sheriff's Department. "It could be natural, lightning, undetermined or it could be human. We don't know."
Temperatures fell a bit and humidity levels rose, helping firefighters deal with what officials have called a monster fire that has killed two firefighters and destroyed 62 homes and still threatened more than 60,000 structures Wednesday night. Since erupting Aug. 26, the Angeles National Forest blaze has burned through nearly 219 square miles and forced thousands of people from their homes.
As of Monday, California had spent $21 million fighting the fire, several media outlets reported.
California Gov. Arnold Schwarzenegger visited the fire area Wednesday, dishing up breakfast for firefighters and giving them protein so "they get all pumped up for the next fight out there with those fires."
Fire officials credit aggressive work for helping to save Mount Wilson, home to a historic observatory and broadcast transmission towers, from taking a direct hit from the fire. Officials said, however, that the observatory and communications complex was still in danger.