Police and firefighters responded to a report of a medical emergency at about 4:10 p.m. at Hunt & Behrens Inc., a livestock feed production facility at 30 Lakeville St., Petaluma police said.
Witnesses told police a 13-year-old boy had accompanied his dad, a local truck driver, to deliver a truckload of grain to Hunt & Behrens. As the father was emptying the trailer of grain, the boy climbed into the trailer for unknown reasons, police said. He became trapped under the grain as it poured out.
The boy's father stopped unloading immediately and worked with others to find his son and pull him out. But when the boy was pulled out, he was no longer breathing.
Paramedics arrived and began trying to resuscitate him, police said. He was taken to Petaluma Valley Hospital where emergency room staff also tried unsuccessfully to revive the boy.
He died about an hour after the accident, police said.
Investigators have not yet released the name of the victim or his father.