A brush at the Kern County line Sunday afternoon burned at least 100 acres by early Monday morning.
Firefighters from at least four agencies including the Los Angeles County Fire Department responded to a brush fire about 1:30 p.m., initially reported as moving uphill through light fuel.
By 3:36 a.m. Monday, all forward progress of the fire was reported, but not until it had burned at least 100 acres at the county line, Fire Department Inspector David Michel said.
Firefighters fighting the same fire in triple digit heat included those Kern County Fire Department and the US Forest Service.
The fire broke out near the northbound lanes of Interstate 5, north of Frasier Mountain Park Road.
No structures were damaged.