It occurred on June 19, 1938 when a bridge, its foundations washed away by a flash flood, collapsed beneath Milwaukee Road's Olympian as it crossed Custer Creek, near Saugus, Montana, south-west of Terry,[1] killing 49 people.
But on the night in question a cloudburst deposited an estimated 4 to 7 inches (100 to 180 mm) of rain on the area drained by the creek.
[6][10] Rescue efforts were mounted by the train crew and uninjured passengers; smashing windows on the partly submerged cars to provide escape routes.
Newspapers reported the paradox that modern air-conditioned rolling stock requiring sealed windows, and the use of shatterproof glass was partially responsible for some deaths.
[11] The investigation determined that the volume and velocity of water flowing beneath the bridge that night was "much in excess of any that had been experienced before or might be anticipated at this place".