Fire agencies so far have spent nearly $50 million fighting the blaze, which was 51 percent surrounded. Full containment was not expected until Sept. 15.
Thousands of firefighters continued work on surrounding the blaze, focusing on the flames' active eastern edge as investigators analyzed clues found at a burnt hillside near Angeles Crest Highway where the fire started. Officials have said the cause of the fire was arson, but have not released any findings.
Because of the deaths of the two firefighters, Los Angeles County authorities opened a homicide investigation after the fire was ruled arson last week. Los Angeles County firefighters Tedmund Hall and Arnaldo Quinones were killed Aug. 30 while seeking an escape route for their inmate fire crew after flames overran their camp on Mount Gleason.
The fire remained a threat to some 5,000 homes and commercial buildings in Monrovia and other foothill communities, but none were in immediate danger. Fire crews planned to light backfires to help destroy fuels if the weather is not too hot and dry, and officials told residents not to be alarmed if they see fresh plumes of smoke.
Crews on Sunday also built protective lines near Highway 39 in the San Gabriel Wilderness, the Forest Service said in a news release.
A break in the high, dry heat also could help the firefighting effort. Forecasts called for higher humidity and fog overnight, and temperatures in the mid-80s on Monday. Crews had been battling the blaze in triple-digit heat last week.
With the decrease in heat, hundreds of firefighters assigned to protect structures have been dismissed. About 4,600 remained.