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
U.S. Route 80 in Arizona was bypassed in 1956 to cross the Colorado River, while the later alignment continued straight ahead into California. Upon crossing the Colorado River to the Fort Yuma Indian Reservation, the older route was still in Arizona. Unlike most of the California and Arizona state border which resides along the Colorado River, the border temporarily cuts north here through the Reservation then east back to the Colorado. This places several acres of land on the western side of the river in Arizona. For a few hundred feet, the state border runs along the western shoulder of pre-1956 US 80. A short