LAST SUMMER, when cracks began to appear in the road to the small Mexican farming town of Santiago Mitlatongo, no one really noticed. Hardly anyone paid attention to the little sinkholes that began forming in the village’s cornfields, or that the deep-rooted sabino trees lining the streets were drying up and slowly dying. Despite this area having been declared an ecological disaster zone by the World Bank, nobody imagined a catastrophe was in the making.

But then, about a year ago, on a sleepy Sunday afternoon a few months after these signs began to appear, the disaster below suddenly announced itself. A cliff above town collapsed, and a torrent of rocks—some the size of two-story houses—rained toward the village below. Within days, the little cracks became vast chasms, and the sinkholes opened their mouths to swallow entire cornfields. Houses began to break in half; some simply sank into the ground and disappeared.

In the weeks that followed, while people were busy salvaging what they could from their toppled houses, they saw that the entire horizon had shifted—the forest above town didn’t quite line up any more, and the road leading out wasn’t just torn up, but no longer even pointed in the right direction. The chasms and sinkholes continued to grow until they formed a vast semicircular tear surrounding the village. Finally, it became clear what had happened: The entire town had broken off from the land around it, and the whole thing was moving—about a yard a day—like a gigantic, land-borne iceberg setting sail on a sea of bedrock. In all, an area of about two square miles—homes, stores, church, and farm fields—was slipping downhill, skidding off its mountain perch like icing off a fallen cake.

Before it began its slide to oblivion, Santiago Mitlatongo, a village of about fifteen hundred people, was like any other in the Mixteca, a rugged, mountainous region straddling the borders of the southern Mexican states of Oaxaca, Guerrero, and Puebla. The region’s high peaks and deep valleys are marked by corn farms, quiet villages, and not much else. Poor and indigenous, isolated from the rest of a rapidly transforming Mexico, and far off the tourist trail, the Mixteca’s strongest connection to the outside world lies in the half-million migrants who have left to seek work in the United States, most never to return. Some villages have lost up to 80 percent of their population and have become little more than ghost towns.

Looking at half-deserted villages surrounded by cornfields eroded down to bedrock, it’s hard to imagine that the Mixteca was once a jewel of Mesoamerica. But this region once sheltered one of the most advanced cultures in the Americas, the only one in the Western Hemisphere with a written history dating back over a thousand years. The birthplace of hundreds of varieties of native corn and some of pre-Columbian Mexico’s most storied fighters, the Mixteca grew into such a powerful region that it was one of the few Mexican kingdoms never to be fully subjugated by the Aztecs. Mixtecapan, they called it: “Place of the Cloud People.”

But today, the “People of the Clouds” have largely drifted away. Few see much future in a place that has lost up to five meters of topsoil to runaway erosion, leaving over 1 million acres so severely damaged that the UN now calls the region one of the most heavily eroded landscapes in the world. One of the oldest continually cultivated patches of ground on earth, tended by one of the world’s oldest farming cultures, is becoming little more than a vacant wasteland.

How could a land that once supported a much larger population, from whose soil had sprouted one of the most advanced cultures in Mexico, fail so miserably? To the extent that the Mixteca’s ecological problems have been examined by outsiders, the list of possible causes feels more like a grab bag of accumulated wisdom than the result of a serious scientific study: droves of grazing sheep introduced by the Spanish, the oxen-powered plow still widely in use, chemical fertilizers and pesticides promoted by the Mexican government, slash-and-burn farming, altered weather patterns from climate change, or just inherently fragile and unstable land.

The source of the Mixteca’s environmental collapse most likely lies in a combination of all of these factors, an accrual of ecological ills meshed against a five-hundred-year history of social upheaval following the Spanish conquest. But to the villagers whose lives have been upended by the erosion of the land, the point is moot, and the directive is clear: get out.

Meanwhile, the town of Santiago Mitlatongo is still moving, a few feet a day, its deserted streets filled with the rubble of toppled-over houses, half a mile from where they once stood.