Time zones in The States can get very complicated, especially in Arizona.
http://en.m.wikipedia.org/wiki/Time_in_the_United_States
Arizona and Hawaii use standard time throughout the year. However:
The Navajo Nation observes DST throughout its entire territory, including the portion that lies in Arizona. But the Hopi Nation, which is entirely surrounded by the Navajo Nation and is entirely in Arizona, does not observe DST. (See map inset right.)