White Sands footprints: people in North America 23,000 years ago

In September 2021, scientists at White Sands National Park in New Mexico announced that human footprints pressed into an old lakeshore were 23,000 to 21,000 years old. That put people in North America at the height of the last ice age, thousands of years earlier than most archaeologists had accepted. The claim was challenged, retested with two independent methods, and held. This U.S. Geological Survey fact sheet tells how.

What archaeologists thought before

For most of the 20th century the first Americans were taken to be the Clovis people, about 13,000 years ago. A few older "pre-Clovis" sites survived intense scrutiny and pushed arrival back to 15,000 or perhaps 16,000 years ago. Claims for anything older stayed controversial.

The place

White Sands lies in the Tularosa Basin of south-central New Mexico, which in the Ice Age held Lake Otero, one of many pluvial lakes across the Southwest. Wind scoured the old lakebed — a process called deflation — and piled its gypsum into the largest gypsum dune field in the world, leaving the flat Alkali Flat behind. Along the edges of the flat, lake and shoreline sediments still show.

Park staff have been finding and recording fossil tracks for nearly twenty years. There are thousands of them: dire wolves, saber-toothed cats, giant ground sloths, camels and mammoths, alongside people. Some trackways run a long way, including the longest back-and-forth human trackway known anywhere, more than 1.5 kilometres. Some show people following in the footsteps of giant ground sloths, and interacting with them.

The dig

At a site on the east edge of Alkali Flat called Locality 2, ground-penetrating radar showed footprints below the surface. A trench exposed them in layers: the team excavated 61 footprints from 8 separate horizons, with thousands more tracks across the park still unstudied.

Most of the prints were made by children and teenagers aged 9 to 14. One explanation is a division of labour: adults did the skilled work, teenagers did the fetching and carrying, and younger children tagged along — so the young left more footprints in the record.

Dating the prints, twice over

Above and below several trackways are thin layers of seeds of spiral ditchgrass (Ruppia cirrhosa). Many of the dated seeds were still on their stems, in crisp layers, so they could not have moved since the plants grew. Radiocarbon dates on them put footprint horizons 2 through 6 between 23,000 and 21,000 years ago — nearly 2,000 years of people at the lake.

Most archaeologists welcomed the result. A few objected: spiral ditchgrass is a water plant, and water plants can take up old carbon dissolved in groundwater, making their radiocarbon ages too old — the hard-water effect.

So the team dated the same layers two other ways:

Both came out statistically indistinguishable from the seed ages (Pigati and others, 2023). The original dates stood.

The pollen also describes the landscape: pine, spruce, fir, oak, sagebrush and weeds — a cooler, wetter country than today, as expected at the Last Glacial Maximum.

Why the prints are there

The layers explain it. At the bottom of the trench, dark gypsum-rich clay is the lake itself. Above it lie lighter gypsum sand and thin clay beds with seeds, laid down by streams and wind — the lake margin. That is where the footprints are. People were not wading in Lake Otero; they were walking a patchwork of wet and dry ground along its shore.

The switch from lake to shoreline was abrupt. The oldest footprint layers, about 23,000 years old, sit near its base, and line up with a sudden warming known as Dansgaard–Oeschger event 2, which began about 23,300 years ago. The warming drew the lake down and exposed a broad shore — and people and animals walked out across it. Geology, hydrology, layering and dates all point the same way: humans were in North America during the Last Glacial Maximum.

Sources

Written from Fossil Footprints and Ice Age Ecosystems of White Sands National Park, by K.B. Springer, J.S. Pigati, D. Bustos, T.M. Urban and M.R. Bennett, U.S. Geological Survey Fact Sheet 2025–3046, a work of the United States government in the public domain. It reports Bennett and others (2021), Science 373: 1528–1531, and Pigati and others (2023), Science 382: 73–75. The authors thank the local Tribal Nations who provided cultural monitoring in the field.