Scattered open flames chewed through brush along hillsides above communities abutting the San Gabriel Mountains as crews doused properties in the path of the fire. Firefighters lit controlled backfires to reduce fuel.
All flare-ups happened within the containment lines of the wildfire that swept through about 2 1/2 square miles of tinder-dry chaparral and destroyed five homes on Thursday, said Incident Commander Mike Wakowski at a morning news conference. The fire was 30 percent contained.
Crews were turning their attention to the fire's north end, to keep flames from moving further into Angeles National Forest.
"Things are progressing nicely," Wakowski said. "It's looking pretty good around the structures."
A huge plume that spread across Los Angeles in the early stages of the fire dissipated but an acrid haze remained.
The National Weather Service said a red-flag warning of extreme fire danger in effect much of the week would remain in place until Friday evening because of low humidity and the chance of the region's notorious Santa Ana winds gusting up to 30 mph in the foothills and canyons.
"The conditions are still extreme out there," said forest supervisor Tom Contreras.
Those conditions come with a bigger backdrop of a serious statewide water shortage and intensifying pressure on Gov. Jerry Brown to declare a drought emergency.
Such a move from Brown, who was planning a "major announcement" for Friday morning in San Francisco, would allow the state to request a broad emergency declaration from President Barack Obama, expediting some water transfers, providing financial assistance and suspending some state and federal regulations.
"Fire season just didn't end this year," Los Angeles County fire Inspector Scott Miller said.
Some 3,700 people from Glendora and Azusa evacuated at the height of the fire, county emergency officials said. Glendora residents were allowed to return home Thursday evening, but homes in Azusa remained under evacuation orders. More than 2,000 people remained evacuated.
Two firefighters had minor injuries and a woman trying to fight the blaze near her home suffered a minor burn, officials said.
Seventeen structures were damaged, including homes, garages, barns and other buildings, he said.
At least 10 renters were left homeless when the fire destroyed rental units on the historic grounds of a retreat that once was the summer estate of the Singer sewing machine family. Statues of Jesus and Mary stood unharmed near the blackened ruins. However, the main, 1920s mansion was spared.
"It's really a miracle that our chapel, our main house is safe," owner Jeania Parayno said.
Three men in their 20s, including a homeless man, were arrested on suspicion of recklessly starting the blaze by tossing paper into a campfire in the forest above Glendora. They could face state or federal charges.
Glendora police Chief Tim Staab said the men were trying to keep warm and the wildfire appears to have been an accident.
"One was very remorseful for starting this fire," he said.
The Angeles National Forest was under "very high" fire danger restrictions, which bar campfires anywhere except in fire rings in designated campgrounds.
The mountains rise thousands of feet above dense subdivisions crammed up against the scenic foothills. Large, expensive homes stand atop brush-choked canyons that offer sweeping views of the suburbs east of Los Angeles.
Whipped by Santa Ana winds, the fire quickly spread into neighborhoods where residents were awakened before dawn Thursday and ordered to leave.
However, other homeowners chose to stay, despite firefighters' orders to get out. Some wore masks against the ash and smoke as they wetted down their properties with garden hoses.
The last catastrophic fire in the San Gabriel Mountains broke out in 2009 and burned for months, blackening 250 square miles, killing two firefighters and destroying more than 200 structures, including 89 homes.
The new fire had abundant fuel to consume. Vegetation above Glendora, an upper-middle-class suburb of about 50,000 people, had not burned since a 1968 fire that was followed by disastrous flooding in 1969.
Many homes are nestled in rugged canyons and ridges that made access difficult.
Hundreds of firefighters were on the scene, along with dozens of engines and a fleet of helicopters and air tankers dropping water and retardant.
The smoke was visible from space in satellite photos. The South Coast Air Quality Management District issued a smoke advisory and urged residents to avoid unnecessary outdoor activities in directly affected areas.
Associated Press writers Christopher Weber, Robert Jablon, Sue Manning, Alex Veiga, and Tami Abdollah in Los Angeles contributed to this report.