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. The Arizona stretch is also known as Mule Creek Road.

Route description
The western terminus of SR 78 is located at a junction with US 191 and SR 75 in Three Way, Arizona near Greenlee County Airport. The highway heads northeast from this intersection along Mule Creek Road. There are multiple hairpin turns along this stretch of highway as it follows the surrounding terrain. State Road 78 heads eastward through the desert, passing through the community of Mule Creek, New Mexico. The road continues eastward until terminating at U.S. Route 180 northwest of Cliff, New Mexico.

History
Arizona section of the highway was designated as SR 78 on February 17, 1959, and the New Mexico section was designated along its current route in the mid-1930s as New Mexico State Road 78.

By 1938, what would eventually become SR 78 on the Arizona side was still just a gravel road as were many roads in the area including US 666. This section would remain a gravel road until 1961. The other state highways in the area were paved by this time including the majority of the New Mexico section. By 1971, nearly the entire highway had been paved with the exception of a portion near the New Mexico-Arizona state line. It was extended to U.S. Route 60 in New Mexico, going through Mogollon, New Mexico, by the mid-1940s and truncated at its present terminus in 1988.