You are mostly correct but slightly imprecise. There is only one Navajo reservation, the Navajo Nation. It is indeed on Mountain time, not Arizona time, meaning it (unlike anywhere else in Arizona) switches to MDT in the summer.
It makes some sense because the Navajo Nation, though mostly located in Arizona, also has a large portion in New Mexico and a smaller one in Utah, both of which observe Mountain time. I don’t know the exact history, but I assume that when Arizona stopped observing DST, the Navajo Nation chose to keep Mountain time to avoid having two different time zones within their border.
The Hopi Reservation, while indeed an enclave within the Navajo Nation, is a completely separate political entity and so under no compulsion to follow any Navajo decisions. Also, they’re entirely within Arizona, so sticking to Arizona time is logical.
Another thing — I can’t recall having ever heard an Arizonan refer to our time zone as MST. That would be technically accurate, but would be confusing because it would naturally imply that we sometimes switch to MDT. We just call it Arizona time, and think of the Mountain and Pacific zones as a separate thing that we’re aligned with for part of the year.
It makes some sense because the Navajo Nation, though mostly located in Arizona, also has a large portion in New Mexico and a smaller one in Utah, both of which observe Mountain time. I don’t know the exact history, but I assume that when Arizona stopped observing DST, the Navajo Nation chose to keep Mountain time to avoid having two different time zones within their border.
The Hopi Reservation, while indeed an enclave within the Navajo Nation, is a completely separate political entity and so under no compulsion to follow any Navajo decisions. Also, they’re entirely within Arizona, so sticking to Arizona time is logical.
Another thing — I can’t recall having ever heard an Arizonan refer to our time zone as MST. That would be technically accurate, but would be confusing because it would naturally imply that we sometimes switch to MDT. We just call it Arizona time, and think of the Mountain and Pacific zones as a separate thing that we’re aligned with for part of the year.