The Rock Shelter That Pushed Oregon Back 18,000 Years

/ Jim
Photo: Bureau of Land Management Oregon and Washington, via Wikimedia Commons (CC BY 2.0)

Outside the little town of Riley, in Oregon’s high desert, there’s a shallow rock overhang called Rimrock Draw Rockshelter. It doesn’t look like the kind of place that rewrites timelines. But the University of Oregon’s archaeological field school, working with the Bureau of Land Management under archaeologist Patrick O’Grady, has been digging there since 2011 — and what came out of the ground suggests people were sheltering there more than 18,000 years ago, thousands of years before the Clovis culture that textbooks used to call the first Americans.

The first shock came in 2012. Digging down, the team found fragments of camel teeth — from Camelops, the extinct North American camel — underneath a layer of volcanic ash from an eruption of Mount St. Helens. The ash was more than 15,000 years old. Anything buried under it had to be older still.

Then came the tools. The excavators uncovered two finely crafted scrapers made of orange agate. The first, found in 2012, still carried preserved bison blood residue. The second turned up in 2015, buried deeper in the ash. And the natural layering of the shelter’s sediments suggests the scrapers are older than both the ash and the camel teeth above them.

The number that made headlines came from the teeth. Radiocarbon dating of the tooth enamel — done first in 2018 and again in 2023 by Thomas W. Stafford Jr. of Stafford Research and John Southon of the University of California, Irvine — returned a date of 18,250 years before present. In O’Grady’s words: “The identification of 15,000-years-old volcanic ash was a shock, then Tom’s 18,000-years old dates on the enamel, with stone tools and flakes below were even more startling.”

Now the honest fine print, because the team itself is careful about it. The 18,250 date is on tooth enamel, not on a tool. The case for people rests on association — stone tools and flakes found in and below the same layers as the dated teeth, in sediments that sat undisturbed under that ash seal. That’s why the university and the BLM phrase it the way they do: the date, in association with stone tools, suggests one of the oldest sites of human occupation in North America. Testing of more camel and bison fragments was still underway when the results were announced in July 2023.

Even with the caution, picture what the layers are saying. While ice sheets still covered much of the continent, somebody in what is now Harney County was knapping orange agate into scrapers, butchering bison and camel, and coming back to the same sheltered spot under the rimrock. We used to think Oregon’s human story started around 14,000 years ago. Rimrock Draw says the first chapter is older — we just hadn’t dug deep enough to read it.

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