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.
Colorado
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. With the decommissioning of the route 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 follows
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.
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