Arson units are investigating the fire's origin, said Los Angeles County Fire Department Inspector Richard Licon.
An 800-acre brush fire in the vicinity of Lake Castaic in the Angeles National Forest was about 60 percent contained Monday, authorities said.
The fire was reported around 2 p.m. Saturday, according to the LACFD.
"Four helicopters are now working on that spot", ANF spokesman Nathan Judy said, noting water-dropping helicopters knocked down the flare up quickly after it started.
Firefighters are gaining good ground on a brush fire that erupted over the weekend at Lake Castiac, but crews are facing scorching temps as they continue their battle.
"Most like the acreage won't change, but the containment will", Judy said, noting there was no large advance for the fire overnight. Two small outbuildings were reportedly destroyed.More news: Options for Supreme Court on Trump travel ban
Firefighters were concerned about the flames spreading due to hot, dry conditions. Information will be updated as it is released and confirmed by fire officials.
Angeles National Forest spokesman Nathan Judy says crews were able to clear brush surrounding the fire to stop its spread and that it appeared they had a handle on it.
Los Angeles County firefighters battled a wildfire by Castaic Lake that grew to about 0.9 of square mile in a remote area. Los Angeles County is experiencing its first major heat wave of the year. There were no injuries reported as of 5:30 p.m.
Four helicopters, five fixed-winged aircraft and one lead air attack are all working together to tackle the blaze.
Some fire resources are being relieved as of 9 a.m. Sunday, but it's more due to the access concerns for vehicles, and a reduced need for structure protection crews where the fire is now burning, according to Nathan Judy of the Angeles National Forest Service.
No mandatory evacuations were in place, Licon said.