One person was found dead and another alive in two cars that plunged 200 feet off a windy mountain road in Southern California.

Los Angeles fire captain Mark Savage said family members found the survivor, a man, at the scene of the crash off Lake Hughes Road in the Angeles National Forest yesterday, after conducting their own search, and alerted authorities.

Capt Savage said officials at the scene were told the man may have been stranded in the vehicle for up to six days.

The injured victim was airlifted to a hospital for treatment.

The crash occurred about one and a half miles south of Warm Springs Rehabilitation, a drug and alcohol abuse treatment centre.

Capt Savage said the California Highway Patrol was taking over the investigation.