I didn't see many trains while in Butte other then what was running, or rather sitting in the Butte, Anaconda and Pacific Railway yards. Interesting operation and one in operation in one form or another since 1892. They did not appear very friendly towards railfans meaning view from afar and /or public property. A request to venture into the still occupied roundhouse was not fruitful.
While in Butte, however, I would highly recommend checking out the former Milwaukee, NP and GN depots. The Milw station is now a television news center. They are very friendly towards railfans.
Butte, Anaconda and Pacific (Rarus)
Don Ross's Butte Anaconda & Pacific site
Butte Montana Milwaukee Road Depot
/Mitch