What Is the World's Largest Gypsum Dunefield?

White Sands National Park in southern New Mexico is the world’s largest gypsum dunefield, stretching across approximately 275 square miles and containing an estimated 4.5 billion tons of brilliant white mineral sand.

What Makes White Sands Different From Any Other Desert

Most deserts are made of quartz sand — ground-down rock and silica worn smooth over millions of years. White Sands is something else entirely. Its dunes are composed almost entirely of gypsum, the same calcium sulfate mineral found in drywall and plaster of Paris. Gypsum is rare as a dune-forming material because it dissolves easily in water, which means it almost never survives long enough in most environments to accumulate at scale. At White Sands, a geological quirk made that survival possible.

Why the Gypsum Stayed: A Basin With No Drain

The Tularosa Basin in southern New Mexico is a closed hydrological system — it has no river outlet to the ocean. Rainwater and snowmelt flow down from the surrounding San Andres and Sacramento Mountains, dissolving gypsum out of the bedrock as they go. That mineral-laden water collects in the basin floor and then simply evaporates under the desert sun, leaving the dissolved gypsum behind as a white crystalline residue. Repeated over thousands of years, this cycle deposited layer upon layer of the mineral with nowhere to escape. The result is a dunefield that holds more gypsum in one place than almost anywhere else on the planet’s surface.

Living Dunes That Swallow Everything in Their Path

The dunes at White Sands are not static. Persistent southwest winds drive the most active formations at rates of up to 30 feet per year — fast enough to bury roads, fence posts, and desert plants with quiet, relentless efficiency. The National Park Service repaves its main road on a regular schedule simply to keep pace. Some plants have adapted by growing upward as the sand rises around them, forming tall pedestals of root and stem. Others are simply consumed. The dunefield is, in the most literal sense, alive and moving.

The Sand That Feels Like Snow

One of gypsum’s most counterintuitive properties is its extremely low thermal conductivity — it absorbs and transfers heat very slowly. On a day when air temperatures reach 100°F (38°C), the surface of the dunes remains cool enough to walk across in bare feet. The sand that looks like a snowfield from the air behaves thermally like one, too. This property makes White Sands one of the few places in North America where you can stand in a blazing desert and feel cold ground beneath your feet.

The Oldest Human Footprints in the Americas

Beneath the surface of the dunefield lies evidence that rewrites the timeline of human history in the Western Hemisphere. In 2021, researchers published findings confirming that fossilized human footprints discovered in the park’s ancient lake bed date to between 21,000 and 23,000 years ago — making them the oldest confirmed human footprints ever found in the Americas. These prints were pressed into the soft mud of a prehistoric lake that once covered the basin floor long before the gypsum dunes existed. The people who left them walked across this landscape during the Last Glacial Maximum, thousands of years earlier than many previous estimates placed the first humans in North America. The dunes that now define White Sands grew up long after those first visitors were gone, sealing the record of their passage beneath billions of tons of white mineral sand.