Temperatures plummeted to minus 27 on Feb. 2, 1989 as 49 runaway train cars barreled down Mullen Pass above Helena. The runaway cars crashed into another train just outside Carroll College.
The crash derailed 15 cars and was followed by two explosions – one from a tank car and one from a nearby transformer station – knocking out electricity and heat to much of the Helena area for several days.
Though nobody was killed or seriously injured, more than $10 million in damages were reported.
Here are photos of the aftermath of this human-caused disaster in Helena.