What is that dark tower along I-90 in western Montana?

I was driving to Seattle from Omaha on I-90. Soon after I left one of the cities, I think either Butte or Missoula, I saw a brown/black tower in the distance on my left. Anybody have an idea what that is?

The only thing I can think of is in Frenchtown. (west of Missoula) It is part of a manufacturing facility.