Air and ground resources battled a brush fire in the Angeles National Forest Monday afternoon.
The Gulch Fire was burning in dry brush next to the San Gabriel Dam, along San Gabriel Canyon Road.
No homes or businesses were immediately threatened by the fire. Caltrans closed Highway 39 north of Azusa, blocking access to San Gabriel Canyon.
Sky5 video showed helicopters making water drops on the fire while other aircraft dropped slurry.
It had burned about 100 acres as of 4 p.m. authorities said. By 10 p.m., the fire was holding at 100 acres, but crews had yet to gain any containment on the blaze.
More than 200 firefighters were assigned to the fire, with many expected to work overnight to set containment lines.
According to the Angeles National Forest, weather conditions were expected to be favorable for firefighters overnight.