US 87 continues in a northwesterly direction in New Mexico, and is signed by NMDOT primarily as an east–west route. It merges with US 64 in Clayton, shortly after entering New Mexico. It continues to the northwest until Des Moines, when it takes a more westerly approach to Raton. In Raton, it separates from US 64 and merges with Interstate 25 and US-85, with which it remains concurrent through Raton Pass and into Colorado, though it is unsigned on much of the concurrency.
Colorado
US 87 remains concurrent with Interstate 25 throughout the state of Colorado, which is a rare occurrence for a US highway to have a concurrency with an Interstate in its entirety within state boundaries. For more on this section of US 87, see Interstate 25 in Colorado.
Wyoming
US 87 remains concurrent with Interstate 25 northward until exit 160 east of Glenrock where it joins US Route 20/US Route 26 from Glenrock to Casper. In Casper it splits from US-20/26 and rejoins I-25 at exit 186. It then remains concurrent with Interstate 25 northward until its terminus with Interstate 90. It then follows I-90 west to exit 44 where it runs up to Sheridan. A portion of US-87 has been washed out for several years along this stretch and "temporary" detour signs are posted directing US-87 traffic along Wyoming Highway 193 through Story. In Sheridan US-87 rejoins Interstate 90 into Montana.
Montana
US 87 remains concurrent with Interstate 90 westward until Billings, where it breaks off and heads north. Between Crow Agency and Billings, US 87 and I-90 are merged with US 212. It intersects with US 12 in Roundup and continues north with a slight bend to the northwest until, at Grass Range it takes a sharp turn to the west at an intersection with Montana State Highway 200. US 87 remains concurrent with Montana State Highway 200 until Great Falls. In Lewistown, it merges with US 191 and remains heading generally west. Some ten miles out of Lewistown, it breaks with US 191 and merges with Montana State Highway 3, heading generally northwest and merging briefly with US 89 before breaking with all three in Great Falls. US 87 heads northeast then east to Fort Benton and then generally northeast to its terminus with US 2 about two miles west of Havre.
Great Falls Bypass
A bypass of US 87 exists on the eastern and northern edge of Great Falls. The route begins at US 87/89 west of Malmstrom Air Force Base along 57th Street South and runs south to north. Just south of the intersection with Second Avenue North the name of the road changes to 57th Street North. At 10th Avenue North, the street name changes to River Drive North, then curves towards the west as it crosses a bridge over a former Milwaukee Roadrailroad line. The route heads straight west until after the intersection of North Park Trail where it curves to the northwest. After a railroad crossing and the entrance to Giant Springs State Park and the Lewis and Clark Interpretive Center, the road curves to the southwest, generally following the south bank of the Missouri River. US 87 Bypass ends at US 87 south of the 15th Street Bridge, but River Drive North continues along the Missouri River through Riverside Park.
History
US Route 87 originally ran northwest out of Great Falls, Montana towards the eastern border of Glacier National Park. US 87 ran to the Canadian Border at the Piegan Border Crossing. This was changed in 1934, when US Route 89 was changed to run over US 87's former routing towards Glacier Park. US 87 ended in Great Falls until around 1945 when it was extended to run to its current northern terminus in Havre, Montana U.S. Route 185 was formed in 1926, and extended from US 85 in Cheyenne north to Orin. It became part of a southern extension and realignment of US 87 in 1936.
