CORONA, Calif. (AP) — A fast-moving brush fire in Southern California’s Cleveland National Forest has grown to 1,200 acres and authorities have issued voluntary evacuations for about 15 to 20 homes closest to the blaze.

Orange County Fire officials say the growth in the fire was expected and none of the evacuation orders are mandatory because no homes are immediately threatened.

Fire Capt. Larry Kurtz says potentially record-setting temperatures in the area and steep terrain are making the fire fight difficult, but there is no wind to contend with.

Nearly 300 firefighters and four water-dropping helicopters are battling the blaze.

Authorities believe the blaze may have started in a backyard but are still investigating.

Cleveland National Forest sprawls over the rugged peaks of the Santa Ana Mountains straddling the Orange and Riverside county line southeast of Los Angeles.

Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.