The remaining 45.27 miles of U.S. 91 in Utah originates at a diverging diamond interchange with I-15/84 at Brigham City. The highway travels east through Brigham Canyon and northeast to Logan and the Idaho state line near Franklin.
U.S. 91 was truncated northward in 1974 and replaced by Interstate 15 and a series of state routes, mostly in urban areas. Through southwest Utah, U.S. 91 entered the state from Arizona via Mohave County Route 91, following what is now Old Highway 91 to Castle Cliff and the Beaver Dam Mountains. The highway climbed onto Utah Hill Summit as it traversed the Beaver Dam Mountains. Old Highway 91 makes a gradual eastern arc, passing through Shivwits and paralleling the Santa Clara River southeast into the cities of Ivins and Santa Clara. Santa Clara Drive extends the former route east to Sunset Boulevard in St. George. The eastern 1.303 miles of Sunset Boulevard are state maintained and designated as Utah 8.
U.S. 91 turned south onto Bluff Street (Utah 18) to St. George Boulevard (Utah 34) east through Downtown St. George. The US highway converged with I-15 just ahead of Red Cliffs Drive. Old U.S. 91 was directly replaced with I-15 northeast across Middleton Black Ridge to where Red Cliffs Drive diverges from the freeway east to Telegraph Street into Washington. All of Telegraph Street northeast to Utah 9 is old U.S. 91. Old Highway 91 resumes in name from there and continues north to eventually run along the east side of Interstate 15 to Leeds.
Page Updated 06-28-2018.