Here's some additional info to add on to what the previous folks have posted.

As noted, NP doubled track Missoula to Garrison in 1909, but in the 1960s NP single tracked it with CTC sidings.

MRL has since done some capacity betterments in the past few years. At Austin, the siding was extended to near the former West Weed location making it approx. 4.5 miles long. The old 6,200 foot siding at Avon was replaced by a new much longer siding to the west named Bradley (but not in the same place as old Bradley), and the 14,000 foot non-CTC siding at Phosphate has been made CTC. Up on the Evaro Hill line (Tenth Sub), the siding at Dixon is now CTC and extended to about 14,000 feet.

As for Homestake Pass line... the previous posts have addressed them. MRL's ownership ends at MP 51 (from Logan). They have this to serve the ballast pit near MP 48. The mothballed portion of Homestake is owned by BNSF, MP 51 to Butte, as well they operate their Copper City Sub, Butte to Garrison.
Dave in MT