Firefighters contained a brush fire near the 118 Freeway in Simi Valley, officials said.
The blaze, dubbed the Kuehner Fire, began about 12:40 p.m. near Rocky Peak Road and grew to 45 acres.
The fire may have been sparked by construction crews working in the area, the California Highway Patrol reported.
The blaze apparently was moving uphill and light fuel was burning, Ventura County Fire Department spokesman Mike Lindbery said in a tweet.
The Ventura County Fire Department responded, with assistance from the Los Angeles city and county firefighters, officials said. Helicopters was making water drops on the blaze.
Correction: An earlier version of this story included an incorrect location of the fire. The story has been updated.