Are there any exposed faults near Butte?
There are literally thousands of faults in western Montana. Most of them are small and formed millions of years ago; only a few dozen faults show any evidence of having moved during geologically recent times (past 2 million years). The most significant fault near Butte trends north-south along the western front of the East Ridge. This fault—the Continental fault—allowed the East Ridge to move up to its present elevation relative to Summit Valley in which Butte sits. Nobody knows when the last earthquake along the Continental fault occurred but the available geological evidence suggests that it was at least several tens of thousands of years ago. The Continental fault is exposed in Montana Resources’ Continental Mine. It is more difficult to see the fault in undisturbed areas along the base of the East Ridge because eons of erosion have washed soil and rocks off the steeper parts of the East Ridge and deposited these materials on top of the fault at the base of the ridge. Interstate 90
