State Route 78 (Arizona–New Mexico) State Route 78 (Arizona–New Mexico) Arizona State Route 78 (SR 78) and New Mexico State Road 78 (NM 78) are a pair of adjoining state highways located in eastern Arizona and western New Mexico linking U.S. Route 191 (US 191) and Arizona State Route 75 near Greenlee County Airport to US 180 northwest of Cliff, New Mexico. It is also known in its Arizona stretch as Mule Creek Road. The western terminus of SR 78 is located at a junction with US 191 and SR 75 at Three Way, Arizona near Greenlee County Airport. The highway heads northeast from this
Arizona State Route 66 line, much of US 66 has been replaced with I-40. Various stretches of the old highway exist as frontage roads and business loops of I-40. In 1984, US 66 was officially removed from the state highway system of Arizona. Most of the old highway had been replaced by I-40, but the portion between Kingman and Seligman where I-40 followed a new alignment to the south became SR 66. In 1990, the state turned over the easternmost of SR 66 (known as Crookton Rd) to Yavapai County for maintenance. Arizona State Route 66 State Route 66 (SR 66) is a surface