The horse and rider were on the tracks near San Fernando Road and Sheldon Street when the train hit them shortly before 4 p.m. Los Angeles City Firefighters say the 38-year-old man and his horse died at the scene.
Two witnesses said they heard the Antelope Valley Train #216 whistle while going southbound on the tracks.
One witness said she saw the rider with a panicked look on his face, trying to jerk the horse's head in the direction of San Fernando Road. The horse panicked when the horn on the train continued and the rider was unable to control the animal.
The witness said the rider looked frightened and frozen when the train hit. The rider was dragged about 75 yards from the horse.
Authorities were still investigating what the rider was doing on the train tracks, as well as why the rider was unable to get off the horse.
No one on board was injured, and buses were sent to shuttle passengers around the area while the train was stopped.