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Expanded excavations at White Sands National Park in New Mexico place humans on the shores of Ice Age Lake Otero between 23,500 and 21,700 years ago, during the Last Glacial Maximum. The same 20 stratigraphic horizons preserve human footprints, megafaunal tracks and travois lines alongside pollen, seeds, leaf-wax isotopes and other climate evidence. Together, they show people moving through a landscape that changed from a perennial lake and conifer woodland to an arid playa and sagebrush–oak steppe, with some swings in water availability occurring within a human lifetime.
What the new White Sands chronology shows
The U.S. Geological Survey’s expanded study assigns the footprint-bearing sequence to 23.5–21.7 thousand years ago (ka). That interval falls at the height of the Last Glacial Maximum, when global ice sheets were largest. Earlier radiocarbon work had already produced an early age for the tracks; the USGS analysis independently refined and reaffirmed it using several materials and stratigraphic relationships.
| Evidence or event | Date or scale | What it establishes |
|---|---|---|
| Footprint-bearing sequence | 23.5–21.7 ka | People repeatedly crossed the former Lake Otero shoreline during the Last Glacial Maximum. |
| Ruppia cirrhosa seeds above and below footprints | 22,860 ±320 and 21,130 ±250 years ago, calibrated ages | Independent aquatic-plant ages bracket layers containing the tracks. |
| Stratigraphic horizons with tracks | 20 horizons | Human and animal activity occurred on multiple preserved surfaces, not a single isolated footprint event. |
| Environmental reconstruction | Approximately 50-year, human-generation resolution | Climate and vegetation changes can be examined at a timescale relevant to people living through them. |
The chronology matters because footprints are direct evidence of people physically present at a specific surface. They do not depend on interpreting whether an artifact was made by humans or whether an artifact layer was later mixed. At White Sands, the human signal and the environmental record are preserved in the same sequence.
How researchers dated the tracks and reconstructed climate
No single measurement carries the entire chronology. Researchers combined radiocarbon dating with stratigraphy and several independent environmental indicators.
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Radiocarbon and stratigraphic checks
New procedures were used to date conifer pollen, while radiocarbon ages from aquatic Ruppia cirrhosa seeds provide bracket dates above and below footprint layers. Sediment position and the order of the layers were tested against those ages. The agreement is why the USGS describes the early chronology as robust rather than relying on one potentially contaminated sample.
Proxies for temperature, water and vegetation
The team counted as many as 75,000 pollen grains in a sample after improved extraction. Pollen identifies the plants growing around Lake Otero; sediment geochemistry and biomarkers add information about the lake and surrounding soils; leaf-wax hydrogen isotopes track changes in water availability. Together with stratigraphic observations, these measurements distinguish a persistent lake from the later playa and resolve changes in aridity and plant communities.
The University of Arizona team reconstructed conditions at roughly a 50-year interval—about the span of a human generation. That resolution is unusually fine for a terrestrial paleoclimate archive in the southwestern United States. It allows short-lived drying and wetting to be separated from the longer retreat of the lake.
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A lake became a playa while people were present
Lake Otero at the Last Glacial Maximum
White Sands was cooler and wetter than it is today. Ice Age Lake Otero occupied the basin, and its shoreline provided a firm route for people and animals. Pollen records indicate conifer forest around the lake during part of this interval.
Rapid aridification and falling water levels
Lake-level evidence from the aquatic plant Ruppia shows rises and falls over approximately 1,500 years before the lake contracted into a flat playa. The environmental sequence records a complete turnover from a perennial lake to that playa. Leaf-wax isotopes indicate that water availability could swing substantially within a century, rather than declining smoothly.
A major aridification episode coincided with Dansgaard–Oeschger event 2 at about 23.2 ka. The same abrupt warming signal appears in Greenland ice cores, linking local drying at White Sands to a broader climate shift. As the lake receded, vegetation changed from conifer forest to sagebrush and oak steppe.
Jessica Tierney, a University of Arizona geosciences professor, said the sediments reveal fluctuations “that were relevant for the humans present at that time.” She also noted that local aridity changes were large and followed global climate shifts. The record therefore captures both long-term lake loss and abrupt variability that could have affected travel, water access, plants and animals.
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What the footprints reveal about people and Ice Age animals
The track surfaces preserve people walking along the lake margin with mammoths, giant sloths, dire wolves and other megafauna. Linear travois features show that people also dragged loads across the shoreline landscape.
Children, teenagers and family movement
Most excavated human tracks appear, from stature and walking speed, to have been made by teenagers and children. One trackway records an adult carrying a toddler. These details turn the site from a simple presence marker into evidence of ordinary movement and caregiving.
Shared pathways with megafauna
One human trackway lies within a giant-sloth trackway, showing that people and the animal used the same surface, though the tracks alone cannot establish how close in time the encounters were. The broader sequence demonstrates repeated coexistence of humans and megafauna around the lake rather than a single dramatic confrontation.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why the site changes the North American timeline
White Sands supports human occupation of North America during the Last Glacial Maximum, thousands of years earlier than the once-common estimate of approximately 13,500–16,000 years ago. The strength of the case comes from the combination of unambiguous footprints, multiple dated materials and environmental proxies in their original stratigraphic positions.
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Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →It also connects a direct human-presence signal to a high-resolution terrestrial climate archive. Researchers can ask not only whether people were present, but what kind of landscape they inhabited and how quickly that landscape changed. Ed Jolie, an anthropology professor and study co-author, said the findings provide scientific evidence consistent with Indigenous peoples’ oral traditions and the understanding that their ancestors have been in the region since time immemorial.
Kathleen Springer, a USGS research geologist and co-lead author, described the goal as expanding the original footprint site and sampling environmental indicators to establish the full context of conditions at the Last Glacial Maximum. She said it is “remarkable” that people in the region witnessed changes discernible within a human lifetime.
What visitors can see now
The original footprint surfaces are currently inaccessible to visitors. White Sands National Park directs the public to a visitor-center exhibit with cast footprints installed in January 2024. The casts provide a view of the track evidence, while the scientific publications and park interpretation explain how the buried layers preserve both human activity and environmental change.
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What remains uncertain
- The dates describe the footprint-bearing sequence and bracketed layers; they do not assign an exact day or year to every individual print.
- Track shape and spacing can indicate stature, walking speed and load carrying, but cannot identify every person or prove the precise timing of an animal–human encounter.
- The climate reconstruction is strongest for conditions represented by the sampled layers. Short fluctuations are visible, but not every annual change is preserved.
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