The Route Fire began Wednesday around noon near Castaic Lake and grew so quickly that a portion of Interstate 5 was shut down in both directions.
"The fire behavior and what you saw yesterday should be a wake-up call to us all about the potential that we're in and we're entering into over the next few days in terms of the fire conditions, very rapid fire growth, and very, very explosive fire behavior," said Angeles National Forest Chief Robert Garcia.
Several evacuation orders were issued Wednesday, though all were lifted by Thursday evening.
"This will be the longest and most intense heat streak so far this calendar year," Alexis Clouser from the National Weather Service in San Francisco told CNN.
Crews prepare for more heat-related health emergencies
Amid the sweltering heat, fire crews focused on "boxing the fire in, reinforcing our fire lines and then anticipating some fire development" due to the high afternoon temperatures, LA County Fire Deputy Chief Thomas Ewald said in the news conference Thursday.
The stifling temperatures were top of mind for officials as they worked to contain the fire but also preserve the safety of those fighting it.
Officials have not disclosed the cause of the fire as it remains under investigation.
More that 500 fire personnel have been deployed to contain the fire, along with 58 fire engines, 8 helicopters and two fixed-wing planes, according to the fire department.
But fires burning elsewhere in the state are forcing officials to split resources, Ewald said.
"There's a large fire burning on the border down in San Diego County, and so those (fixed-wing) aircraft are being pulled off of these fires," he said. "There's homes being lost in that area and so the priorities shift throughout the day. ... We ordered more fixed wing but some of those aircraft are being diverted to that fire."