The Sharp Fire had burned 150 acres by 7 a.m. Saturday. It was 40 percent contained.
Authorities said the fire started about noon Thursday in a steep area only accessible by air or by hiking. As helicopters dropped water on hot spots trying to put out the flames, the DC-10 air tanker was also in the air dropping Phos-Chek.
"The Phos-Chek is a form of fire retardant, and while it does not put the fire out, it buys the ground crews time to come in and reinforce those retardant lines with actual hand line or wet line," said San Bernardino County Fire Department spokesman Eric Sherwin.
Firefighters are making good progress on the ground, but it's slow, hard work considering how steep and rocky the terrain is in the area.
Forest fires are something people in the area know is part of the program when you live in the mountains.
"You've got to expect that there's going to be a pretty good-size fire about every four years or so. I've been up here almost 20 (years), and there's been some pretty good ones in that time," said Wrightwood resident Russ Urquidi. "I've been evacuated once, and some people evacuated right now, so hopefully nobody else will be evacuated."
Mandatory evacuations were ordered for Mojave Scenic and East Canyon drives south from Loan Pine Canyon Road to Buckthorn Road, Slippery Elm and Mahogany roads. About 100 homes were evacuated. No structures have been damaged.
An evacuation center was set up at Serrano High School at 9292 Sheep Creek Road in Phelan.
At least 380 firefighters were on scene Friday. Two firefighters suffered minor injuries.
The cause of the fire remains under investigation.