It was in the late 1990s when I first began to see Mixtec migrants in the farm fields around my hometown in California's Central Valley. The Mixtecs, or Ñuu Savi, were once one of the great civilizations of meso-America, but they were pushed out by collapsing corn prices and severe land erosion. Now, they were here—just a few hours north of Los Angeles—coming like so many groups before them, to provide the labor that fuels California's multi-billion dollar agricultural machine.

When I started photographing this migration about a decade ago, there were approximately 50,000 indigenous Mexican migrants in the U.S. Now the number is closer to 500,000. In California, Mixtec has become the state's most widely spoken indigenous language. In Mexico, I have visited dozens of Mixtec communities that have lost so many people to migration; they have become ghost towns.

There are plenty of villains to blame for the disappearance of this ancient culture—the Green Revolution, NAFTA, or the unrelenting march of globalization. As I have watched this exodus unfold, I keep coming back to the land. "The land is my mother and father," a woman in Mexico told me. "It talks to me just like a person would." As the People of Clouds scatter to the wind, it's that connection to the land. That's what we're losing.