Arizona is in the Mountain Time Zone, according to the Arizona State Library. It is one of few places in the United States that does not observe daylight-saving time, so Arizona is on Mountain Standard Time year round.
Arizona observed daylight-saving time on several occasions, usually during wartime, since 1918. However, most of the state returned to Mountain Standard Time on Oct. 29, 1967. The Navajo Nation in the northeastern part of Arizona continues to observe daylight-saving time, as of 2014.
Daylight-saving time originated with Benjamin Franklin's idea that adjusting the time to take advantage of daylight hours would conserve energy.