A sport utility vehicle traveling westbound in the eastbound lanes of Interstate 90 just west of Garrison struck an oncoming pickup, killing the passenger.
The Montana Highway Patrol says the collision shortly after noon on Tuesday killed a 57-year-old Ronan woman. Her name hasn't been released.
The victim's husband suffered minor injuries, as did the 41-year-old Idaho man who was driving the SUV.
Patrol dispatchers had no information on whether the SUV driver was cited or arrested.