FRAZIER PARK, Calif. — Firefighters battled terrain and flames as they worked to surround a wildfire burning for a third day in harsh hills and mountains north of Los Angeles.

Thirty miles to the south, firefighters worked to save 19 mountain homes in a 250-acre blaze.

Temperatures dipped Thursday and remained cool Friday, but winds exceeding 20 mph continued to swirl. Much of the Frazier Park blaze that has blackened more than 6 square miles was in rocky, rugged, difficult-to-reach places, making containment a challenge.

After a heavy aerial firefighting effort, the blaze was 35 percent contained Friday.

In Castaic to the south, a fire started just before 1:30 p.m. Friday and briefly threatened an elementary school.

Firefighters in the air and on the ground were able to douse the flames closest to Northlake Hills Elementary School.

The school had a large defensible space around it, so it was easy to protect, Los Angeles County Fire Inspector Scott Miller said.

The campus was put on lockdown and buses were put on standby for a time in case hundreds of kindergarten through fifth-grade students needed to be evacuated.

After the flames were redirected, Los Angeles County sheriff's Sgt. Brian Allen said the students were released to their parents without incident.

Although the fire was still some distance from the homes on Elk Ridge Road and Vista Point Place, Miller said residents were asked to leave as a precaution.

The fire was moving toward Castaic Lake.

The cause of the fire is still under investigation.

The Frazier Park fire broke out near Interstate 5 on Wednesday when temperatures were in the 80s, and though they have since cooled, winds have continued to be a problem.

"It's definitely gusty, but we're lucky, the winds are blowing away from homes," Kern County Fire Department spokesman Corey Wilford said Friday. "It would be better if we didn't have winds at all though."

Lower temperatures were expected to persist into the weekend.

The fire has spread to three counties - Los Angeles, Kern and Ventura - but burned in mostly unpopulated areas and threatened no homes or buildings.

A Kern County high school was closed as a precaution.

The fire initially burned thick brush, seasonal grasses and sage, but then moved into trees.

The cooler weather helped firefighters overnight clear brush and create breaks in hopes of slowing the blaze. Efforts Thursday were focused on the southern edge of the fire.

The cause of that fire was also under investigation.