Been a while since I was around Butte, so some of the current info may be wrong.

Rarus (old BA&P) and Montana Western (NP Butte to Garrison) were owned by the same two families, each running on railroad. All the power was maintained by the Rarus at the old B&AP shops in Anaconda, though Montana Western crews ran out of Butte. In the 90s, Rarus was busy hauling slag out, and had several projects where dirty dirt was hauled out of the Butte/Silver Bow area up towards a new haz mat dump below Anaconda that even included a new spur and highway xing. Montana Western was busy usually making two trips a day with 3-5 old MW/Rarus Geeps and 30-70 cars each train, mostly bridge traffic between UP at Silver Bow and MRL/BN at Garrison. Both MW and Rarus had local customers in the Silver Bow/Butte area.

BN/BNSF then decided to set rates that weren't attractive to using the UP Silver Bow MW Garrison MRL routing, so almost overnight most of MW's overhead traffic dried up. There was a clash between owners and employees, and the employees went union. The owning families sued BN/BNSF over the lost traffic and they ended up settling and buying the railroad back. A little while later, Rarus was sold to Patriot Rail who quickly reassigned the extra engines that Rarus had plus scrapping much of the old equipment left around the Anaconda shops. I know OERM got some stuff, and at least one car?

I'm not sure, but I think BNSF kept Montana Western as a subsidiary. It made it easier and likely cheaper just to accept the existing union contracts and keep the same crews working out of Butte. The last I knew a couple BNSF geeps were assigned and rotated out via MRL for repair or inspection.

The Port of Silver Bow has their own switch engine, as does the local grain elevator. I think that odd GP38 you saw was the Port of Silver Bow's. If you search the various railroad photo blogs I think you will find I am fairly close.

That whole area just doesn't see near the rail it did in the 90s, most of the UP-MW-MRL bridge traffic is gone, Eastern Idaho out of Idaho Falls used to run four jobs M-F plus one on Saturdays, and Pocatello was still a working hump yard with a PFE shop. Up used to run a fruit train M_F night that left Idaho Falls about midnight with EIRR and their local traffic, at Pokey more perishable cars were added including from EIRR at Twin Falls and as far as Nampa, sometimes even Hinkle, before heading east with potatoes, frozen food and other perishables.