Archaeologists from the University of Oregon’s Museum of Natural and Cultural History Archaeological Field School have been excavating the Rimrock Draw Rockshelter site near Riley, for over a decade.

Testing of artifacts done earlier this year indicates that the team has found one of the oldest sites of human-occupation in North America.

Patrick O’Grady, the archaeologist leading the project, said he has been drawn to this location for a long time.

”And then the site that we’re working on is extraordinary,” he said.

“Just because it is so old, but the things that we’re finding, the sediments, the stratigraphic layers, the archaeology, is very consistent. Usually, you’re picking together and putting together bits and pieces of the past that are scrambled.”

In 2012, O’Grady and his team discovered a clean layer of volcanic ash from a Mount St. Helens eruption that happened 15,300 years ago. Soon afterward, the team found a concentration of large animal teeth.

“(The teeth) were clearly big enough to not be anything that exists on the landscape today,” said O’Grady. “We weren’t sure exactly what it was, but given the size it was probably something along the lines of camel tooth enamel.”

Underneath the enamel, the team discovered an orange agate scraper that wasn’t naturally occurring, he said.

“It was clearly a tool that had been fashioned by humans,” said O’Grady. “The flaking patterns are so distinctive on it that it couldn’t have been naturally created.”

O’Grady began to have the samples identified. He said he was surprised to learn the volcanic ash was as old as it was. The tooth find did turn out to be camel tooth enamel, after a radiocarbon dating analysis done in 2018. In that same analysis, the enamel was dated to 18,250 years ago, which was in the Pleistocene era.

“That’s pretty scary stuff for an archaeologist because that suggests you have a pretty old site, one of the oldest in the country perhaps,” O’Grady said.

Evidence at the Cooper’s Ferry archaeological site in Idaho suggests human occupation goes back over 16,000 years. It is currently known as the oldest site in western North America.

Partnership with the Bureau of Land Management

O’Grady first came across the rockshelter site when Scott Thomas, an archaeologist with the Bureau of Land Management, was doing a study of Paleo-American sites, which are in the 7,000 to 14,000-year-old range, that they were both interested in.

The Rimrock Draw Rockshelter happened to be one of those sites.

The university began working on the site in 2011 under a partnership agreement with the bureau.

Typically, the bureau doesn’t deal with excavations, but instead turns its attention to finding sites and working with resources.

“When we find an important site, we usually try to do a partnership, and this one was with University of Oregon, and, you know, they’ve been out there for over 10 years now,” said David Holst, an archaeologist who works for the bureau.

He said archaeological sites are either completely excavated, especially if the site is going to be majorly impacted, or they are only excavated to a certain point to be preserved for future studies.

“It’s hard to find these intact sites like this. That’s what makes them unique. It’s that there has to be good site preservation,” he said.

Holst said he hopes the recent discoveries bring archaeologists together to “rewrite some of this early human migration.”

It is unknown when humans came to North America

Tom Stafford, who performed the radiocarbon dating analysis, said in an email, “We have obtained ages several thousands of years older than for commonly accepted human sites in North America and we are inviting comments, criticism, and further radiocarbon testing to evaluate our hypotheses.”

Stafford said scientists are still debating the origins of the first humans in North America — when they arrived and where they came from.

“Whether one is an archaeologist, geologist or paleontologist, we are trying to interpret human and geological events whose evidence has been largely erased by the the passage of time,” he said. “We are trying to interpret an evanescent record that becomes increasingly sparse with increasing geologic age.”

Stafford said he believes archaeological digs in ancient marshes and streams in Oregon have been overlooked, and that they contain evidence of human presence.

“A century of spectacular discoveries awaits us,” he said.

Building up evidence

The pandemic slowed O’Grady’s efforts to get his team’s finds dated. He had the camel tooth enamel dated again, and the dates that were given in February 2023 were roughly the same. There was some slight variation that actually dated the enamel to be even older, said O’Grady.

“That allows us to open up a conversation about what is the oldest date that we can see at the site thus far, and start working forward from that with some additional dating,” he said.

O’Grady’s team also began excavating at different sections of the site, to see if the dates matched up. Amazingly, they did.

“At this place we have archaeological deposits that suggest what happened at one portion of the site is what happened at the other, and that’s just such a rare thing,” said O’Grady.

The last time the archaeological school was at the site, in 2021, a team member discovered a full camel incisor, though without a root.

The discovery was made on the last day of the dig.

Now, the archaeological school is back at the site, and ready to get started.

“We’re out here prepping the site and getting ready to excavate in that unit….We’re ready to go but we can’t quite take off yet,” he said.

O’Grady’s team will be excavating the site through the beginning of August.

“To be able to put students on archaeology that’s this old and this complex, it’s just a treat,” said O’Grady. “We’ve always taken quite a bit of pride in working on sites that students may never experience again in their career, or if they do it’s going to be an exceptional career.”