“Not so. Arizona has been this way for a long time.”
As I recall, AZ stays on Standard Time year round. It does create some interesting things though. You can fly from Phoenix to Las Vegas in the Summer and arrive before the time you left because the flight takes less than an hour!
In the summer, AZ (except for the Navajo Reservation) and NV are on the same time. It may work that way in the winter, when NV goes back to PST and AZ remains on MST.