It goes northeast and intersects Colorado State Highway 113 southwest of Iliff.

It becomes more easterly as it goes through Iliff, Proctor and Crook, where it intersects Colorado State Highway 55.

It continues on to Sedgwick, where it meets Colorado State Highway 59.

[citation needed] Shortly after entering Nebraska, U.S. 138 intersects Interstate 80.

At Big Springs, U.S. 138 turns north and ends at U.S. Highway 30.