Archaeologists have found evidence that humans occupied a site near the Eastern Oregon town of Riley more than 18,000 years ago.
The discovery — which has been called “startling” — was made in the Rimrock Draw Rockshelter by archaeologist Dr Patrick O’Grady of the University of Oregon and his colleagues.
In the rockshelter, the team have found both stone tools and tooth fragments from extinct species of bison and camel that date back to the late Pleistocene epoch.
Radiocarbon dating of enamel in the tooth fragments indicated that they came from 18,323 years ago — meaning that the tools, found in a deeper sediment layer, must be older still.
This suggests that the Rimrock Draw Rockshelter may be the oldest-known site of human occupation in North America, pushing the archaeological record back by more than 2,000 years.
Professor David Lewis is an anthropologist at the Oregon State University who undertook his doctoral studies at the University of Oregon.
He said: “This early date aligns well with the oral histories of the tribal nations in the region, many of whom have stories about witnessing geological events like the Missoula floods.”
These, he explained, were “a series of events that changed everything for the tribes between 18,000 and 15,000 years ago.
“As well, tribes have oral histories of encountering giant animals, monsters on the land, and Rimrock Draw rock shelter’s evidence suggest that we did interact with the megafauna.
“They may have become characters in our histories of the time before memory.”
The researchers have been undertaking excavations at the site since 2011, thanks to a partnership agreement with the Bureau of Land Management.
It was in 2012 that Dr O’Grady and his team found camel teeth fragments at the site, buried below a layer of volcanic ash deposited by an eruption of Mount St. Helens more than 15,000 years ago.
Digging deeper — and thus also going further back into the archaeological record — the researchers also unearthed two finely crafted orange agate scrapers, one in 2012 and the other in 2015.
The former, the researchers noted, still retained a residue of bison blood on it, hinting at how the tool would once have been used.
Dr O’Grady said: “The identification of 15,000-years-old volcanic ash was a shock, then [the] 18,000-years-old dates on the enamel — with stone tools and flakes below — were even more startling.
The archaeologists are planning further investigations of the Rimrock Draw Rockshelter and the finds it has already yielded.
Additional testing of other camel and bison tooth fragments is presently underway, they explained, while archaeobotanists are studying plant remains from cooking fires traces at the site.
And this summer will see Dr O’Grady complete his final archaeology field school at the rockshelter, with more Ice Age animal remains and artifacts to work on.
Heather Ulrich — Oregon/Washington archaeology lead at the Bureau of Land Management (BLM) — said: “This is a very exciting development for the archaeological community.
“Previous excavations on BLM public lands in Oregon have provided archaeological evidence of human occupation dating back 14,000 years.
“Thanks to the partnership with Dr O’Grady and the university, these new dates push our archaeological knowledge of human occupation in North America even farther, perhaps the oldest yet.”
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