Filed Under Environment

Intersection of BA&P Trail with Montana St.

As you approach the bridge below Montana Street, you can see rock outcrops mostly on the south side of the trail. You should notice fractures in the granite that trend about east-west, nearly parallel to the trail. The major ore-bearing veins in the area (Butte’s “main-stage” veins) intruded the granite along these fractures. You can see some brownish-red stained veins here that were once ore-bearing closer to the bridge.


Untitled Overview of the trail, looking east toward the Montana Street bridge. The nearly vertical fractures on the right are the fracture system along which ore-bearing veins were intruded into the Butte granite.
Untitled The light and dark-speckled granite near the bridge was intruded by a light-colored vein of aplite – a non-ore bearing vein composed of light-colored minerals. This rock can be hard and does not tend to deteriorate. Many rock walls and foundations are made up of this rock type. One of the best examples of a building constructed mostly with this stone is at 117 North Excelsior Avenue.


Location: Latitude 46.01800 Longitude -112.54067


Larry Smith, “Intersection of BA&P Trail with Montana St.,” Story of Butte, accessed April 14, 2024,