The whole idea of DST is that by turning your clocks ahead or back, you can take advantage of the natural sunlight and save on energy. But, Arizona is sunny anyway - really sunny. And in the summer, let's face it, Arizona can be downright hot. So, adding additional sunshine hours to the day doesn't help.

 

Wikipedia explains why:
Arizona observed DST in 1967 under the Uniform Time Act because the state legislature did not enact an exemption statute that year. In March 1968, the DST exemption statute was enacted and the state of Arizona has not observed DST since 1967 (however, the large Navajo Indian Reservation, which extends from Arizona into two adjacent states, does). This is in large part due to energy conservation: Phoenix and Tucson are hotter than any other large U.S. metropolitan area during the summer, resulting in more power usage from air conditioning units and evaporative coolers in homes and businesses. An extra hour of sunlight while people are active would cause people to run their cooling systems longer, thereby using more energy.

 

Local residents remember the summer of 1967, the one year DST was observed. The State Senate Majority leader at the time owned drive-in movie theaters and was nearly bankrupted by the practice. Movies could not start until 22:00 at the height of summer: well past normal hours for most Arizona residents. There has never been any serious consideration of reversing the exemption.

 

For those of you not in Arizona, don't forget to move your clocks back an hour at 2 a.m. on November 1st.