The fire, dubbed the Zebra Fire, was reported at about 7 p.m. near Highway 39 and Mountain Laurel Way. Highway 39 was closed at Sierra Madre while crews battled the brush fire.
Officials with the Angeles National Forest said no homes were threatened. The fire was burning away from homes, up a steep hill near the mouth of the San Gabriel Canyon.
Brush fire in Azusa grows to 25 acres, prompts closure of Highway 39
Still, people in the area sent video to ABC7, which shows just how close the flames were burning.
Water-dropping helicopters were brough in to extinguish the flames.
It's unclear what started the blaze, but fire officials remain on high alert as a heat wave and chance of thunderstorms increases the risk of fires.
Even if there is no rain, ABC7 meteorologist Carley Gomez says there is still a threat for dry lightning.
"When we see a lot of lightning strikes, they do happen to be in the mountain spots. That's because there's a lot of trees there. There's also towers, sometimes wind turbines in our deserts, and those are good catalysts to produce a lot of lighting strikes as that storm system moves right ton through," she said.
An Extreme Heat Warning will remain in effect for a large swatch of the region through Thursday.
City News Service contributed to this report.