FALLBROOK, Calif. (AP) — California's newest wildfire tore through retirement communities built on golf courses and killed elite thoroughbred horses in its first destructive day.

The new blaze in San Diego County means a huge swath of Southern California is now in flames. December's shockingly dry, hot and windy conditions brought on unprecedented fire danger.

The San Diego-area fire quickly grew to more than 6 square miles and burned dozens of homes at Rancho Monserate Country Club.

Flames engulfed a horse training center, prompting trainers to unlock stables and encourage hundreds of race horses to run for their lives. It's not clear how many died.

The region's biggest fire, which is 200 miles north, keeps growing and has destroyed more than 400 homes and buildings.