The 1,952-acre fire had been 78% contained Sunday as crews continued to cut lines in steep terrain. Officials expect to have the blaze fully contained by Wednesday, according to the U.S. Forest Service.
The blaze broke out shortly before 6 a.m. Thursday and has destroyed at least five homes and 11 other structures. At least six other structures have been damaged.
For days, the flames were fueled by high temperatures, dry weather and strong winds after an illegal campfire sparked by three men in their 20s near Colby Trail and Glendora Mountain Road got out of control, authorities said.
The men, who were arrested not long after the fire started, will likely face federal charges, said Glendora Police Chief Tim Staab.
Forest Service officials said steep terrain and low humidity were the main obstacles facing more than 1,000 firefighters still in the field.