Firefighters worked throughout the night to keep the blaze, dubbed the Madre Fire, under control. On Wednesday, crews will continue to mop up.
The brush fire broke out around 6 p.m. Monday near San Gabriel Canyon Road and Sierra Madre Avenue. Three firefighters received minor injuries, but authorities say they have been treated and are already back on the line.
Full containment is expected by Friday morning, an official said, who added that there were hot spots but no active flames.
Highway 39 is open to residents only.