Interstate 15 is the only north-south interstate highway in Montana. Beginning at the Canadian border crossing at Sweetgrass, it goes south through
Shelby and
Conrad to
Great Falls. From
Great Falls, its direction is south and slightly west through
Helena and on to
Butte. For about 10 miles west of
Butte, it coincides with
Interstate 90. Going south again, it crosses Deer Lodge Pass, goes through
Dillon and finally enters
Idaho at the Monida Pass.
Plan your vacation to the Pacific Northwest with 
