The victim, 75, was walking his Labrador retriever in Del Mar, Calif., without a leash near train tracks. When the conductor of an approaching train saw the man and his dog he sounded the horn to warn them.
San Diego County Sheriff's deputies said the sound of the horn startled the animal and it began running toward the tracks, the Los Angeles Times reported.
The man ran after the dog and into the path of the train. He was declared dead on the scene.
The dog was not hurt. Deputies located the animal a short distance away and returned it to the man's family.