The fire was only about 5 percent contained Monday afternoon, authorities said, and could take a week to bring under control, the Los Angeles Times reported.
Dubbed the Williams fire, the blaze started Sunday afternoon in the San Gabriel Mountains between Camp Williams Resort and Burro Canyon Shooting Park. The fire was moving north toward Rattlesnake Canyon, but was not endangering any structures.
To contain the fire, about 48 crews are working by hand in steep and rugged terrain to dig up vegetation to create a wide strip of bare earth.
Among the injured, two firefighters have been treated for heat-related ailments. A third person hurt an ankle. None of the injuries has required hospitalization.
Six helicopters and several air tankers were assisting firefighters.
A separate fire that started Monday in the Los Padres National Forest was reported under control after it had burned about 30 acres in the Lockwood Valley area.
In northwest Nebraska, firefighters reduced three wildfires that had burned nearly 214 square miles, the Omaha (Neb.) World-Herald reported.
The Wellnitz fire, which began in Nebraska and moved north into the Pine Ridge Indian Reservation in South Dakota, was 27 percent contained, said a spokesman for the Nebraska Emergency Management Agency.
Firefighters claimed the 58,450-acre West Ash fire near Chadron and the 29,730-acre Douthit fire near Crawford were 75 percent contained.