Just after 8 o’clock one spring morning, 2,000 feet below the rim of the Grand Canyon, Nate Chamberlain, wearing chaps and cowboy boots, emerged from the post office in Supai, Arizona, with the last of the morning mail. He tucked a Priority Mail envelope into a plastic U.S. Postal Service crate lashed to one of the six mules waiting outside. Then he climbed into the saddle on the lead mule, gave a kick of his spurs, and set off down the dirt road leading out of the village …

Supai, the only village on the reservation of the Havasupai Tribe, is one of the most remote communities in the country. It is accessible only by foot, and by helicopter when the weather allows. The mule train, which makes the 16-mile, six-hour loop up and down the canyon five days a week, is perhaps the most extreme manifestation of the USPS mandate to “render postal services to all communities.” Mail delivery in Supai involves a feat of logistics, horsemanship, and carefully placed hooves … It also offers a glimpse into what the Postal Service can mean for rural America, at a moment when the agency’s future is uncertain.