The county seat of Deer Lodge is Anaconda. Does that ring a bell?
It's all about the Anaconda Copper Company. Anaconda effectively screwed over its eponymous city and the nearby city of Butte. They left it with the Berkeley Pit, a massive, sprawling copper mine and now-Superfund site that has turned the landscape into a barren, desolate area - a depressing contrast to the beautiful surrounding areas.
To put it simply, the areas are Democratic because they were economically depressed in the 1980s and people remember. Unemployment exceeded 20 percent. A good description can be found in The Profits of Doom
, which was published in Atlantic Monthly
Unemployment has since fallen, but the area is still a wasteland. It's improving, certainly, but people are still upset and there is a very strong anti-corporate movement. Anaconda, on the other hand, seems fairly better off and still remains quite beautiful, but scars remain. It'll be interesting to see if the area remains so Democratic as time goes by.