U.S. Route 6 in Utah

The road from SR-1 (US-91 by 1926, now US-89) in Spanish Fork southeast via Price and Green River to the Colorado state line became a state highway in 1912, with the final section - Spanish Fork to Colton - being added in May.[15] However, the original route was somewhat longer than present-day US-6, most notably between Price and Green River, where travelers went south from Price to Castle Dale via present SR-10 and then east to Green River via what are now county roads north of the San Rafael River (partly along an old never-used Denver and Rio Grande Railroad grade[16]). Other differences included going southeast from Green River to Valley City and northeast to Thompsons.[17] New construction through Price Canyon between Kyune and Castle Gate was made easier by the presence of the Denver and Rio Grande Railroad in the canyon.[18][19] Later that year, the Midland Trail Association was organized in Grand Junction, Colorado to promote a transcontinental auto trail that would include this road.[20]

A 1913 law provided state aid to counties to construct the Midland Trail, with a general route defined. Initially it was to follow the present US-6 via Woodside between Price and Green River, but an amendment changed it to the existing state road through Buckhorn Flat (east of Castle Dale).[21][22] Travelers began using the Midland Trail through eastern Utah in early July 1913, and the road through Price Canyon, replacing a detour via Willow Creek Canyon (US-191) and Emma Park,[23] was completed by the men of Price later that month.[24] A.L. Westgard of the National Highways Association praised the improvements to the road since the previous year, singling out the Price Canyon segment as "almost beyond comprehension".[25] Although it was hoped that it would become part of the Lincoln Highway, the high mountain passes in Colorado convinced that association to designate a route farther north through Wyoming in September 1913. Midland Trail promoters were not discouraged; instead they were determined to continue to improve to the route to make it better than the Lincoln Highway.[26]

The shorter route via Woodside rather than Castle Dale was considered again in 1916, due to problems with maintaining the latter and a new bridge over the Price River at Woodside,[27] and it was adopted as a state road in April. The piece northwest of Sunnyside Junction had already been designated as part of a state road to Sunnyside, the rest of which still exists as SR-123. A cutoff from Springville south to Moark Junction via Mapleton was also added that year.[28]

A 1919 law redefined the state highway system to include only a short list of roads and any federal aid projects. At the urging of Grand County, the route that corresponded to the Midland Trail was realigned to the longer but more scenic road along the Colorado River between Moab and Cisco, including the new Dewey Bridge.[29][30][31] In response to a Carbon County request, the law also removed Price Canyon from the route, instead taking it along the older road through Willow Creek Canyon and Emma Park.[32] Finally, the older route from Spanish Fork to Moark Junction was dropped in favor of the 1916 addition from Springville.[33] Four years later, both counties had changed their minds,[34] and the legislature changed the route back. The Moab-Cisco River Road was entirely dropped (though it was redesignated in the early 1930s as SR-128), but both the Price Canyon and Emma Park routes remained.[35] Also that year, the Bureau of Public Roads approved Utah's seven percent federal-aid system in accordance with the Federal Aid Highway Act of 1921, including the Springville-Colorado segment of the Midland Trail.[36]

In the 1920s, the State Road Commission numbered the Springville-Colorado roadway as State Route 8.[37] Several years later, in 1926, it also became part of U.S. Route 50, which continued east to Annapolis, Maryland (west of Thistle, the road was initially not part of US-50; instead it was the north end of US-89, which ended at Spanish Fork, leaving the Moark Junction-Springville road as simply SR-8).[11][38][39] The legislature officially adopted the SR-8 designation in 1927, dropping the Emma Park alternate, and designating two other roads as SR-8: the Spanish Fork-Moark Junction road, which had been dropped in 1919, and a branch from Soldier Creek Junction northeast via Nine Mile Canyon to Myton,[40] which had been part of the 1919 system.[41] The Myton spur was split off in 1931 as SR-53,[42] and the Spanish Fork spur became SR-105 in 1945.[43] In 1962, SR-8 was truncated to Green River, with the section east of Green River transferred to SR-4. In 1963, SR-8 extended north to north of Lehi, replacing part of SR-1, which was rerouted on current I-15 as that was constructed. In 1964, SR-105 became part of an extended SR-26. In 1969, the section east of Moark Junction became part of SR-27, leaving SR-8 as the legislative designation for US-89 from north of Lehi to Moark Junction. SR-8, SR-27, and SR-4 were cancelled in the 1977 Utah state route renumbering.

The state completely reconstructed US-50 east of Spanish Fork in 1930 and 1931, eliminating most curves and railroad grade crossings, and shortening it by 14 miles (23 km).[44][45]

[46]

The Grand Central Highway was the local name for the road beginning at the Lincoln Highway in Ely, Nevada and running east and northeast through Delta and Eureka to the Arrowhead Trail in Santaquin.[47] Due to its avoidance of the Great Salt Lake Desert that the Lincoln Highway passed through, Ely garage owners were promoting it as the best route to Salt Lake City by May 1921.[48] For the same reason - long stretches of desert - Grand Central Highway promoters believed it to be superior to the Arrowhead Trail for Los Angeles-bound travelers.[49] The Eureka Commercial Club posted a billboard in Santaquin in July, advertising the "shortest and best all year route to California".[50] The Midland Trail Association, whose trail followed the Lincoln Highway's route between Salt Lake City and Ely, adopted the Grand Central as an official alternate route in June 1922.[51] The next year, the state legislature added the road from Santaquin to Silver City (southwest of Eureka) to the state highway system,[52] and in 1925 it was extended to Delta.[53] Along with the road southeast from Delta to Holden, this was designated State Route 26 in 1927, and at the same time the road west from Delta to Nevada was added to the system as State Route 27.[54] (The portion in Nevada became SR 14 in 1925.[55])

In 1925, during early U.S. Highway system planning, the Grand Central Highway was designated as U.S. Route 50's path across western Utah.[56][57] However, when the final plan was approved in late 1926, US-50 had a gap between Ely and Thistle.[38][39] The gap was filled in about 1930 - but via the Wendover Cutoff, far to the north, leaving the Grand Central Highway as only SR-26 and SR-27.[58] The road again received attention in 1932, when the Roosevelt Highway Association was looking for a path for a westward extension of its trail - which had survived the 1920s by being identified with U.S. Route 6 - from Greeley, Colorado to the West Coast. The association tentatively approved a route in April, entering Utah via US-50 to the Utah Valley, and leaving via the Grand Central Highway to Ely. The Delta Lions Club had suggested this alignment for the same reasons that the highway had become popular in the 1920s: cooler weather than the Arrowhead Trail (then US-91).[59] Despite the State Road Commission designating US-40 across the state as the Roosevelt Highway in 1935,[60] the final route, approved by the American Association of State Highway Officials as US-6 in December 1936, followed US-50 and the Grand Central Highway.[10]

However, the designation did not mean that the road would be immediately improved. It was not until September 1952 that paving was completed west of Delta, largely on a new alignment south of the old road. Business Week described the original route as "nothing but a wagon trail-rutted, filled with dust...one of the worst chunks of federal [sic] road in the country." A two-day celebration was held in Delta to mark the occasion.[12]

The town of Dividend was bypassed by a new route through Homansville Canyon in about 1931, and the old route (Dividend Road) initially became a branch of SR-26.[61] It was renumbered State Route 159 in 1945[62] and deleted from the state highway system in 1969.[63] In 1965, SR-26 extended east to SR-8, replacing SR-105. In 1969, SR-27 extended east to Green River, replacing part of SR-26 and part of SR-8.

In April 1983, a massive landslide occurred along the US-6 and US-89 concurrency near Thistle, which closed the highway for eight months. When the highway reopened, it had been substantially rerouted, with US-6 being routed onto a higher alignment. US-89 continued to use part of the original US-6 alignment, but in the opposite direction.

Prior to 1995, US-6 passed directly through the cities of Payson, Salem, and Spanish Fork along what is now SR-198, and the four-lane expressway that ran from I-15 at Spanish Fork southeast to Moark Junction was known as State Route 214.[64][65] However, in 1995 US-6 was moved onto SR-214, completely eliminating that route and introducing a concurrency with Interstate 15. The old alignment between Santaquin and Moark Junction became a new SR-198.[66]