U.S. 89 begins at Flagstaff, Arizona. The highway proceeds north passing near Grand Canyon National Park and through the Navajo Nation. Near the Utah state line the highway splits into U.S. 89 and U.S. Route 89A. The Alternate is the original highway; what is now the main highway was constructed in the 1960s to serve the Glen Canyon Dam. The two highways rejoin in Kanab, Utah.
The main branch passes over the Colorado River just south of the Glen Canyon Dam and Lake Powell near Page then enters Utah. The Alternate branch crosses the Colorado River at Navajo Bridge and proceeds to the North Rim of the Grand Canyon before entering Utah.
Prior to 1992, the southern terminus of US 89 was at Nogales, Arizona. US 89 ran concurrently with Interstate 19 (I-19) until Green Valley. The route was taken (in a northerly direction) through Tucson via 6th Avenue, Congress Street and Granada Avenue. The route was carried out of Tucson via State Route 77 (SR 77). Further north it was carried via the Pinal Pioneer Parkway northwest out of Oracle Junction on SR 79. In Maricopa County, it ran concurrently with existing US 60 along Main Street in Mesa, Apache Boulevard and Mill Avenue in Tempe, then along Van Buren Street in Phoenix to Grand Avenue, then to Wickenburg. Departing Wickenburg, it followed US 93 and SR 89 to Prescott. Departing Prescott, the route followed present-day SR 89 to Ash Fork, then ran east concurrently with I-40 to Flagstaff.
In Flagstaff, US 89 ran along old Route 66, Milton Road and Santa Fe Avenue. The highway crossed the Little Colorado River at Cameron on the Cameron Suspension Bridge until 1959, when the bridge was retired and replaced by a parallel span.