GLENDORA, Calif. — It could be a week before firefighters can contain a 3,600-acre blaze in the Angeles National Forest because of high temperatures and rugged terrain in thick brush that has not burned in a couple of decades.
The cause of the fire that started Sunday afternoon in the San Gabriel Mountains, spoiling holiday hiking and camping plans for thousands, has not been determined, the California Department of Forestry and Fire Protection said.
A burned car was found in the area, but it is not clear if it started the fire or was just destroyed by it, officials said.
No structures have burned. Five minor firefighter injuries have been reported, four for heat and one twisted ankle, said Calfire Incident Commander James Smith. No one has been hospitalized.
Fire conditions early Tuesday were good, with temperatures in the upper 60s, 6-mile-per-hour winds, and humidity at 20 percent, Smith said.
Campgrounds that typically attract up to 12,000 visitors on the holiday weekend, as well as rehabilitation centers and a private mobile home community of Camp Williams Resort, were evacuated Sunday, but some people stuck around.
‘‘Twenty-five people have elected to stay in place regardless of the evacuation order,’’ Smith said.
Daniel Burress, 68, known to park residents as ‘‘Grandpa,’’ said he has never evacuated, even when wildfires were far closer.
‘‘I’m a Vietnam vet,’’ Burress told the Los Angeles Times. ‘‘So this doesn’t scare me at all.’’
Officials said campgrounds, although not in the line of the fire, had to be emptied so the only road in and out of the San Gabriel Canyon could be open just for fire trucks and emergency vehicles.
The area burned is about 5½ square miles. The latest update Tuesday estimated the fire to be 15 percent contained, Smith said.
The reason it will take so long to circle the fire is because the basic firefight is taking place from the air, Captain Roland Spreewell told KTTV-TV. ‘‘It’s hard to get boots on the ground’’ because of the conditions, he said, explaining that much of the area had slopes of 30 to 80 degrees.
There is a chance of precipitation in the area in the next week, but those chances are not great, said meteorologist Mike Wofford.