It happened at the first falls area in Eaton Canyon north of Pasadena about 6:30 p.m. Sunday.
Officials said the 26-year-old man was hiking when he lost his footing and fell down a steep hillside.
Witnesses called for help for the injured man. The Los Angeles County and Pasadena fire departments came to his rescue.
The man was flown to Huntington Memorial Hospital. His condition was not immediately known, but it was later reported the man was pronounced dead at the hospital. He was identified as Erwin Molina.