Arizona is on Mountain Standard Time. Arizona does not observe Daylight Saving Time, with the exception of the Navajo Nation. Arizona previously observed Daylight Saving Time beginning in 1918, but made the permanent change to Standard time in 1968.
Time zones in the United States developed in the mid-nineteenth century to accommodate railroad schedules, which required standardizing time across the nation. Before the adoption of time zones, local communities each observed their own time schedules.