The Earthquakes of Nineteen Thirty-Five

The first major shock hit on October eighteenth, nineteen thirty-five, at approximately ten forty-eight in the evening. Helena residents felt the ground move and heard the masonry crack, but the damage seemed survivable. Then the aftershocks kept coming, and the city began to understand it was not dealing with a single event.

The earthquake swarm of nineteen thirty-five was one of the most prolonged seismic sequences in Montana's recorded history. The strongest shock registered magnitude six point two on the modern scale. A second major earthquake struck on October thirty-first, Halloween night, and in some ways it was worse than the first because it hit already-damaged buildings that had not been repaired or demolished in the intervening weeks.

Two people died. Four were killed in total across both major shocks and their aftershocks. The property damage was staggering for a small city: estimates at the time reached four million dollars, equivalent to many times that figure today. More than two thousand buildings in Helena sustained damage. Many of the Gilded Age sandstone structures that had survived forty years cracked through their foundations or lost their upper stories.

The earthquakes exposed something about Helena's urban fabric that the city's founders had not accounted for: the same geological forces that brought gold to the surface in Last Chance Gulch also put the city on active fault systems. The Big Belt Mountains to the east and the ranges framing the Helena Valley are products of the same Basin and Range extension that periodically moves the ground beneath the city.

Federal relief funds under the Works Progress Administration helped Helena rebuild and repair. The Cathedral of Saint Helena, still under its original construction debt in nineteen thirty-five, survived both shocks, though its towers sustained damage that would not be fully addressed for another fifty years.