The northern route is the original alignment. It was used until about 1899 when the railroad determined that standard gauging this route would be too difficult. It moved the route further south.
The original route was converted into a highway. In the early 1960s highway officials felt that route was too tough as many truckers experienced the same hair-raising decents as train crews did earlier. A route even further north was constructed, which is the current route.
The dirt road (some pavement remains) begins a few miles east of the summit, travels around the muleshoe curve (narrow gauge version of horseshoe)up the hill to the summit. It rejoins the current road a few miles north of the summit.
The current road passes the old helper station of Russell. CDOT has some sand storage there for the winter.
The road rejoins the railroad as Wagon Creek.