Technically, Arizona is on MST all year. Utah and others are on MST (Mountain Standard Time) half the year and MDT (Mountain Daylight Time) half the year, which is an hour ahead.
Similarly California spends half the year on PST and half in PDT…which is the same time as MST.
So it’s technically correct to say Arizona is on MST the whole year…but it’s misleading to many who view that as Mountain Time and know that Arizona is on Pacific Time equivalent for half the year