Firefighters stopped the forward progress of a brush fire above Azusa on Tuesday evening after it had charred about 40 acres.
The blaze was 10% contained after breaking out in the Fish Canyon area in the San Gabriel Mountains, fire officials said.
An inmate working on a hand crew sustained a minor injury, the Los Angeles Fire Department said.
Earlier, firefighters on the ground were being aided by water-dropping helicopters as hand crews cut fire breaks around the perimeter of the blaze, the Fire Department said.
Two Super Scooper aircraft were dispatched but cancelled shortly before 4 p.m. by fire commanders as crews appeared to make headway in stopping the blaze.