A Prehistoric Mystery, Rewritten

Deep within an ancient sinkhole lie the remains of dozens of mammoths — prehistoric wanderers who waded into warm springs to their deaths. For decades, those deaths were accepted as having occurred roughly 26,000 years ago. But new research published in the journal Quaternary Research suggests these ice-age giants were actually more than 160,000 years old. That’s not a minor correction. It’s a seismic shift in our understanding of one of the most significant fossil sites in the world.

Researchers from The Mammoth Site of Hot Springs, South Dakota, published the results of their study using infrared-stimulated luminescence to re-date the site, arriving at a new age range of 160,000 to 232,000 years ago. The paper was published in Quaternary Research on August 11, 2026. The findings don’t just push back a date on a calendar — they reframe the entire story of what this place was and when it existed.

What Went Wrong With the Old Dates

Early radiocarbon dating on mammoth bone apatite yielded ages around 26,000 years BP, but these results are now considered unreliable due to contamination from groundwater and young carbon introduced by artesian flow. In other words, the warm springs that lured the mammoths to their deaths may also be responsible for corrupting the very evidence scientists used to date those deaths. It’s a cruel irony buried in the geology.

Jim Mead, an emeritus researcher at Mammoth Site and the University of Arizona, had doubted the old dates for years. Having worked as a graduate student in the University of Arizona’s radiocarbon lab, Mead found the dates researchers got from the mineral part of bone — called apatite — to be unusual. He said, “I have always wanted to get a different chronology method to date the site… and a decade later here we are.” His persistence ultimately paid off in a big way.

Researchers analyzed six samples from the bone bed using infrared-stimulated luminescence on feldspars, because the quartz luminescence was saturated; the ages ranged from approximately 232,000 to 160,000 years ago, showing better agreement with previous uranium-series and thermoluminescence analyses. Luminescence dating is a type of radiation exposure dating that determines the age of sediment grains based on their last exposure to light or intense heat.

One of North America’s Greatest Fossil Sites

The Mammoth Site was discovered by accident when work on a housing project revealed a collection of giant tusks. Soon after, Mead and the late Larry Agenbroad — a former professor at Northern Arizona University and site director — got to work digging up one bone after another. Their investigations revealed an ancient sinkhole likely formed when the ground above collapsed as underlying groundwater slowly dissolved the supporting rock.

The world’s largest mammoth research facility and one of the top fossil interpretive sites in North America, over 60 mammoths — 58 Columbian and 3 woolly — have been unearthed, along with at least 87 other Late Ice Age animals. What makes it especially remarkable is that the mammoths found there appear to be almost entirely male and mostly young — the greatest concentration of Columbian mammoths anywhere in North America.

What This Changes Going Forward

The new luminescence dates suggest these mammoths lived in a far deeper, likely colder chapter of the Pleistocene, making the site one of a rare few dated so deep into the Northern Great Plains’ past. That context matters enormously. A site from 160,000–232,000 years ago tells a fundamentally different story about mammoth migration, climate, and ecosystem than one from 26,000 years ago.

Researchers said the findings open the door to exploring questions about mammoth history over a broader time span and may prompt a re-evaluation of the Black Hills’ Ice Age. As site principal investigator Dr. Chris Jass put it, “The re-dating of the Mammoth Site suggests that the site is over 100,000 years older than we once thought. At a broad level, the work reflects the importance of continuing to test previous interpretations and really highlights the significance of our preservation of much of the site in situ.” Science, it turns out, doesn’t just dig up bones — it keeps digging up better questions.