SH 172 begins in the south at the New Mexico state line where the road becomes NM 511.

From there, the route travels through the Southern Ute Indian Reservation northward through Ignacio where it meets the western end of SH 151.

From Ignacio, the road gradually arcs to the west and passes westward through Falfa before again turning northward to meet its northern end at a junction with US 160 approximately eight miles southeast of Durango.

The southern end of the road was changed to the New Mexico state line by 1972.

Media related to Colorado State Highway 172 at Wikimedia Commons