On July 6, 2017 GRMI, the seismometer in the geology lab of Calkins, recorded a magnitude 5.8 earthquake near Helena in western Montana. Buried in the seismic trace of the larger earthquake were two aftershocks, one measuring 4.9 and the other 4.5 in magnitude. In the seismogram, we can see many aftershocks associated with the magnitude 5.8 earthquake. This swarm of earthquakes occurred as the result of strike-slip (horizontal) faulting along the Lewis and Clark line, a broad zone of faulting about 400 km in length, and up to 80 km wide that extends from Helena, Montana southwest into eastern Idaho. Other notable events from the Lewis and Clark line include the August 1959, magnitude 7.2 Hebgen Lake earthquake, the largest historic earthquake in this region. The Hebgen Lake earthquake triggered a massive landslide that resulted in more than 28 fatalities, mostly in campgrounds around the lake. Fortunately, this most recent quake caused only minor damage and no reported injuries. For more information about the earthquake visit the U.S. Geological Survey’s website.
The daily employee newsletter of Grand Rapids Community College 
In the 1990’s my wife (born and raised in Billings, MT), her father, and I were trout fishing along the banks of Hebgen Lake. We were about 20 yards apart, set our lines, and were sitting on the ground. We all felt something going up our spines, looked at each other (confirming what we had felt), and knew it had been a tremor.
We have visited multiple times, the room at Montana Tech in Butte, MT which houses the equipment recording the hundreds of seismic sensors in Montana. It is fascinating as you realize there are tremors (mostly small) going on constantly in the State of Montana.
That is very cool, Dan. We visited Hebgen Lake in the summer of 2014, it’s a fascinating place.