The eastern terminus of SR 266 is located on US 191 south of Safford. The highway heads southwest from this intersection before curving towards the west. It briefly curves towards the northwest before curving back towards the west and arriving in Fort Grant. The highway continues towards the west to its western terminus in Bonita. SR 266 has a spur route that heads north from the highway to the prison at Fort Grant just prior to the highway's western terminus. SR 266 travels through sparsely populated areas and does not pass through any cities or towns. It serves primarily as an access road to Fort Grant.
