State Route 66, or AZ-66 is a surface-road in Mohave and Coconino counties in northwestern Arizona, USA. The road continues east into Yavapai county as a county-maintained road that is not officially part of the state highway system. State Route 66 is a relic of the former U.S. Route 66, and is the only part of old US 66 in Arizona to have Arizona state highway markers. Its western terminus is near Kingman at exit 52 on Interstate 40 and its eastern terminus lies near Seligman at exit 123 on Interstate 40.
State Route 66 tends downward toward the west, with the vegetation becoming more desert-like toward Kingman. The terrain changes at a slower pace than the more direct Interstate 40, making it a scenic alternative at the cost of some time. It still serves communities that the freeway avoids, including Valentine and Peach Springs; it enters the Hualapai Indian Reservation. For those willing to take the time to appreciate the scenery, it is a good alternative to the high-speed freeway.