Kelley Mine

What did the mine headframes in Butte do and which ones remain?
What did the mine headframes in Butte do and which ones remain?
What did the mine headframes in Butte do and which ones remain?
You see them every time you drive through Butte. They kinda look like buildings, but they're not. And they're all over the hill. They all look relatively similar yet upon closer inspection there are subtle differences. What in the world are these behemoth structures?