U.S. Route 50 in Utah

In 1926, when the U.S. Highway system was first announced, there was a gap in US-50 between Ely and Thistle.[8] At the time the states of Utah and Nevada were feuding about which of the old auto trails would be paved and used for the new U.S. Highway System. Nevada favored the Lincoln Highway, which the modern US-50 closely follows in that state. Utah refused to consider the Lincoln Highway west of Salt Lake City. Officials perceived that route would carry all California bound traffic directly to Nevada while passing through very few communities in Utah. Utah instead favored the Victory Highway (modern Interstate 80 west of Salt Lake) and the Arrowhead Trail (modern Interstate 15). By favoring these routes Utah could force travelers destined for southern California to use a different route than those destined for northern California, with both of these traversing through more cities in Utah than the Lincoln Highway. The Arrowhead trail was especially beneficial to Utah as it passed through many communities in the state, but only Las Vegas in Nevada.[9]

Utah prevailed and US-50 did not continue to follow the Lincoln Highway to Salt Lake City as Nevada had wanted. The first continuous route of US-50 across eastern Nevada and western Utah was an arch shaped route. US-50 proceeded north from Ely along what is now numbered U.S. Route 93 and Alternate US-93 where the highway would merge with the Victory Highway (U.S. Route 40 along the Wendover Cut-off, since replaced by I-80) to Salt Lake. From there the highway returned to Green River via what is now numbered State Route 201, U.S. Route 89 and U.S. Route 6.[10]

The second iteration has its origins with the formation of US-6. In 1937, US-6 was extended west from its former terminus at Greeley, Colorado to Long Beach, California.[11][12] In eastern Utah the route used the existing alignment of US-50. However, in western Utah the route used an unpaved road through Delta reconnecting with US-50 in Ely.[10] In 1953, US-50 was approved to use this shorter alignment with the older US-50 alignment designated as U.S. Route 50 Alternate.[13] Nevada first showed this alignment as paved and signed as US 50 in their 1954 map.[14] With this change, US-6/50 ran concurrent from Ely to Grand Junction, Colorado.

The paved version did not exactly follow the unpaved roads. The dirt route passed through the numerous mountain ranges of the Great Basin using Marjum canyon and Marjum Pass to and through the Tule Valley. Once paved, the route was relocated to follow the north shore of Sevier Lake, which reduced the number of mountain ranges crossed.[2] Although US-50 was moved to yet another alignment, this route remains US-6 today.

The modern route of US-50 was created in 1976.[15][16] This iteration of US-50 has its origins in a dispute over the route of Interstate 70 in Utah. While I-70 was in the planning stage Colorado lobbied for an extension of the original proposal to run across Colorado and into Utah. Utah supported an extension using then US-6/50 to connect Denver, Colorado with Salt Lake City. However, federal planners did not see value in this route and instead supported a route that could be used to connect Denver with Los Angeles, California. I-70 was built using the federally selected route.[17] In 1976, US-50 was changed again to a routing mostly concurrent with I-70. The portion of modern US-50 between Delta and Scipio had been previously numbered State Route 26,[15] and the portion between Scipio and Salina had been numbered State Route 63, with the SR-63 portion being transferred to SR-26 in 1971.[18]

East of Green River I-70 closely follows the original route of US-50, with some minor straightening by Crescent Junction, Cisco, and Westwater.[2]