Last week, Americans set their clocks back one hour in the familiar “falling back” ritual that ends daylight saving time. Well, some of us did. Others, who tell time in the digital age via computer and smartphone only, probably had the time reset automatically for them. And some Americans didn’t have to reset a thing, because they never “sprang forward” back in March at all. Hawaii doesn’t observe daylight saving time, for example. Neither does Arizona—well, except for the Daylight Saving Donut.

The northeast corner of Arizona belongs to the Navajo Nation. The reservation covers 27,425 square miles, an area larger than West Virginia. That makes it by far the largest Native American jurisdiction in the country, covering the entire Four Corners area, including parts of Utah and New Mexico.

Arizona hasn’t observed Daylight Saving Time since 1967, mostly due to energy conservation. Giving Arizonans more sunlight in the summer is like donating water to the passengers aboard the sinking Titanic: They’ve already got plenty, thanks. Arizona saves millions of dollars in cooling costs by staying on Mountain Standard Time year-round.

The Navajo Nation, however, includes parts of two states that do observe summer time. Rather than putting neighboring Navajo communities on two different clocks, the reservation has elected to adopt daylight saving time even though most of their land lies within Arizona. It’s the only part of Arizona that changes its clocks in the summer. But here’s the tricky part: The Navajo nation completely surrounds the smaller Hopi Reservation, which is entirely within Arizona. The Hopi, like the rest of Arizona, have no reason to switch to daylight saving time, so they don’t. The Arizona portion of the Navajo Nation is, therefore, sometimes called the Daylight Saving Donut: a ring of noon surrounded both outside and inside by 11 a.m.