From Daily Mail (caution: tabloid):
An earthquake struck near Malmstrom Air Force Base in Montana, which oversees a large network of intercontinental ballistic missile (ICBM) silos spread across the state.
The US Geological Survey (USGS) recorded a 4.2 magnitude quake at 12:41pm MT (2:41pm ET), just seven miles outside of the center of the base located in Great Falls. Hundreds of people in the area reported shaking, with one saying on X: ‘We just had an earthquake, holy cow, our building shook, looks like we were very close.