Firefighters on Sunday were battling a 100-acre brush fire in the Angeles National Forest above Azusa.
The fire was at Mile Marker 24 on Highway 39, according to the Los Angeles County Fire Department. Smoke could be seen for miles. No structures were immediately threatened.
KTLA News reported that Highway 39 has been closed.
Fire officials said they have assign air crews to the blaze, and CalFire is assisting L.A. County fire.
Officials noted conditions in the area were hot and muggy.