In my area of NE Montana, there were several spur lines built to service a big construction project and then had the tracks pulled up when the project was finished. When the bridge across the Missouri River was built, they first built a rail spur from Macon to the bridge site. A big shuttle track now serves the grain and fertilizer plant that occupy the old Macon elevator. Because I know where the old spur was, I can still pick out a couple dirt mounds where the rail used to be but 100 years erased most of the traces. There was also a spur from Nashua, MT to the site of the Fort Peck Dam. Rail was used to haul in a lot of goods and equipment used to build the dam. That same spur was used to close off the river flow when they dumped fill from the rail in the middle of what is now the berm that makes up the dam. About the latest spur I can think of is the one that ran from Glasgow, MT to the site of the old SAC USAF base that sits NE of the town of Glasgow. That one would have been built in the 1950s but the cross ties and rail are gone now. The grade is still pretty visible.