The man was taking a cigarette break when the male and female pit bulls attacked him shortly after noon, said Sgt. Dennis Gutierrez of the Riverside County Sheriff's Department.
The man, who was the grandfather of the dogs' owner, died at the scene. His name was not released.
County Animal Services spokesman John Welsh said the dogs were euthanized later in the afternoon. The male dog weighed 107 pounds and was about 3 years old, while the female weighed 52 pounds and was about 6 years old.
Welsh said it was unclear why the dogs suddenly attacked the man, who was familiar with them and had played with them before. But he noted that neither dog had been spayed.
"Unaltered dogs are always more aggressive," Welsh said. "We always recommend that for family pets, people spay or neuter their dogs."
Gutierrez called the incident a "vicious attack and very tragic for the family right before the holidays."