According to Montana Highway Patrol, a 70-year old Dillon resident was riding in a Ford pick-up truck with a 38-year old Bozeman man just after 6 am on Friday.
The pair were driving north on Highway 41, and slowed to turn left near mile marker 26.
MHP dispatchers said a vehicle behind the pick-up swerved right into the shoulder to avoid hitting the truck. But a semi was in the process of passing both vehicles, and couldn't stop in time.
They said the semi T-boned the truck, and the pick-up rolled.
The 70 year old passenger was ejected and died. He was the only occupant between all the vehicles not wearing a seat belt.
The Bozeman driver sustained non life-threatening injuries, and semi driver was unharmed.