Central Corridor (Union Pacific Railroad)

Proceeding east out of Winnemucca, the route follows the Humboldt River, in a directional running setup with the Overland Route until Wells, Nevada.[1] From Wells to Salt Lake, the route, known as the Shafter Subdivision, loosely follows the historical route of the Hastings Cutoff, tunneling underneath the Pequop Mountains and crossing the Toano Range via Silver Zone Pass. The eastern approach to Silver Zone Pass features a near 360 degree horseshoe curve known as the Arnold loop. After crossing these mountain ranges the route proceeds southwest towards the Great Salt Lake Desert. In Nevada, Interstate 80 follows the Central Corridor, though the two routes are several miles apart in places.[2]

The route enters Utah at Wendover and crosses the Great Salt Lake Desert and the Bonneville Salt Flats, parallel to Interstate 80 and the Wendover Cut-off, en route to the southern shore of the Great Salt Lake and Salt Lake City. Upon reaching Salt Lake City, the line turns south and follows the Jordan River through Point of the Mountain towards Spanish Fork.

After Spanish Fork, the rail line joins the U.S. Route 6 corridor, and the two follow each other towards Denver. Both routes follow the Spanish Fork (river) up a grade in the Wasatch Plateau, cresting at Soldier Summit. The western approach to Soldier Summit is known for the Gilluly loops, a series of horseshoe curves that allow the railroad to crest the mountains while maintaining grade that never exceeds 2.4%, unlike the highway, which was built using an older railroad grade, that features grades in excess of 5%.[3] The railroad descends from Soldier Summit following the Price River until reaching the town of Helper, so named because in the era of steam locomotives, the railroad added or removed helper engines here for trains crossing Soldier Summit. Upon exiting the Wasatch Mountains, the train follows the southern rim of the Book Cliffs, in route serving the towns of Woodside, Green River (where the rail line crosses the Green River), Thompson Springs and Cisco. Near Cisco is where the rail line for the first time meets the Colorado River, which provides the path up the Rocky Mountains in Colorado. The rail line follows and crosses the river numerous times in Colorado while ascending the Rockies. Ruby Canyon is where the rail line reaches the state line.

The railroad enters Colorado along the north bank of the Colorado River, following the river to the Grand Valley, passing through the heart of Grand Junction and surrounding cities along the way. The tracks continue to follow the river out of the valley, routed along Debeque Canyon, Glenwood Canyon and Gore Canyon of the Colorado River towards Granby, Colorado near the headwaters of the river. The railroad departs the main stem of the Colorado river to follow the Fraser River, one of its tributaries until reaching the crest of the Rocky Mountains which is surmounted via the Moffat Tunnel. Aside from the now-dormant line over Tennessee Pass, the Moffat Tunnel is the highest point on the Union Pacific System.[4]

The eastern descent from the Moffat Tunnel towards the Front Range, where Denver resides, features 33 tunnels, leading to this portion commonly called the tunnel district. This portion of the tracks loosely follow modern Colorado State Highway 72, though at points the two corridors are in different canyons and several miles apart. Even past where the tracks exit the Rocky Mountains, the grade features horseshoe curves in the final descent. The tracks approach the Denver metropolitan area from the northwest, before merging with other rail lines just north of downtown Denver.