A bit more of the story. Where we were stopped was the the side of a mountain. On the uphill side was a similarly-stopped freight train, with an oil tanker car

A bit more of the story. Where we were stopped was the the side of a mountain. On the uphill side was a similarly-stopped freight train, with an oil tanker car right next to us. Below us was a raging, flooded, river (on account of the same storms that washed out the track). And up above was a cliff, with a boulder on top that seemed maybe a little precarious. So we were sitting there wondering if the same storm that eroded the tracks had maybe eroded the cliff around that boulder, allowing it to tumble down through the oil tanker to send us plunging into the flood waters below. Brooding over that was less fun than the distraction of the sing-along.