An overview of the Rimrock Draw Rockshelter site in Harney County. Stone tools found at the site date back more than 18,000 years, making them some of the oldest evidence of human habitation in North America.
Provided by the University of Oregon Museum of Natural and Cultural History
Oregon archaeologists have found evidence of human occupation in the state that dates back more than 18,000 years. University of Oregon students and faculty working at the Rimrock Draw Rockshelter in Harney County found stone tools and fragments of camel and bison teeth beneath a 15,000-year-old layer of volcanic ash. Radiocarbon dating of the tooth enamel revealed that the fragments were 18,250 years old. Due to their position in the ash, the tools are thought to be even older — making them some of the oldest evidence of human civilization in North America.
Joining us with more details about the discovery is Pat O’Grady, a staff archaeologist at the University of Oregon Museum of Natural and Cultural History.
The following transcript was created by a computer and edited by a volunteer:
Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. Six years ago, the New York Times reported that the earliest widely accepted evidence of people in the Americas was no more than 15,000 years old, but that date has now been pushed back further into the past. And much of the evidence comes from the Pacific Northwest. Oregon archaeologists have found stone tools that date back more than 18,000 years, meaning what is now Harney County has among the oldest evidence of human civilization in North America.
Pat O’Grady has been overseeing a lot of this work. He’s a staff archaeologist at the University of Oregon’s Museum of Natural and Cultural History and he joins us now from the site. Pat O’Grady, welcome.
Pat O’Grady: Good afternoon. Thanks for having me.
Miller: Can you describe just where you are now? What does the Rimrock Draw Rockshelter look like right now?
O’Grady: Right now, I am sitting on a terrace across an ancient stream channel from Rockshelter that is about 20 meters long. It’s a very modest piece of basalt that sticks up above the landscape and it’s in a wide open arid desert terrain. So it’s a place where the wind blows from the southwest and winds carry sediments that have come over the top of the ridge and down behind the basalt wall and accumulated sediments for what looks like about 18,000 years.
Miller: What might it have been like 18,000 years ago?
O’Grady: At that time we’re thinking about this in terms of the end of the Pleistocene, the Pleistocene was the great Ice Age that started to level off and the conditions warmed at that time. It was still cold and very wet, a very tough place to live. But it was also a time when the ice sheets across North America began to thaw and we see lots of water moving through different systems at that time and very different types of vegetation, not just sagebrush and juniper like we see today.
Miller: And is the idea that this might have been some kind of a shelter, a way to get away from rain or wind or, I don’t know, blowing sand?
O’Grady: That’s about it. I’ve been back here in February when it’s freezing cold but the sun’s out, and because the wind is coming from behind the Rockshelter, the air is still and it’s just really quite comfortable back there. It’s not very deep, it’s only about three or four meters deep from the roof into the back of the Rockshelter area. So it was a place to get out of the rain and away from the wind, but not a place where people lived for extended periods of time.
Miller: When you are there in that shelter in February, I mean, are you imagining what it might have been like for another human 18,000 years ago to do the same thing?
O’Grady: All the time. I think that’s a primary driver for archaeologists is what was it like for people back in those times? And when we find artifacts that are buried in a place like this, it’s almost like you touch hands across the pond. You’re making connections over great expanses, many thousands of years and meeting those people firsthand.
Miller: How is this site chosen for a dig? I mean, you’re in a place in Harney County in Southeast Oregon, and for anybody who either lives there or has traveled through there, one of the most inescapable facts about so much of Oregon is just its vastness and unpeopledness right now. You can go for miles and miles and not see anyone and see in some ways what seems like an unchanging landscape. In all that vastness how do you decide which places to put out the grid and to very, very carefully dig?
O’Grady: That’s a great question, and a great deal of that credit belongs to Scott Thomas, who is our district archaeologist with the Burns BLM. He’s retired now, but he and I have been working archaeology in this area since 2007. We’ve been focused primarily on Paleo American sites, or those sites that date from about 7,000 years back in time to 18,000 [years].
Scott and I have spent a lot of time covering this terrain and he was here for decades as the BLM archaeologist. And so we know that the area where this site is located is one that in general has very old sites and not more recent sites. And so that’s been a puzzle for quite some time, one we’ve been fascinated with trying to sort out. And so we focused our efforts on looking at several sites in this area. And then when Scott was driving to help us bring supplies to one of them, he spotted a little fold in the basalt out on an open landscape and stopped to have a look and then discovered a very unique setting that looked like a very important place.
Miller: Let’s talk about time here. And time before now. What was the assumption for the date of humans being there, passing through or spending time there at the very beginning? How old did you think it was?
O’Grady: What we’re seeing when we first started looking at this site were stone tools that are called projectile points and they fit into the Western Stemmed tradition, which is a distinct group of projectile points. They’re fairly large and they have long blades. The business end is pretty long, and then they have weak shoulders and a rounded base that’s distinct. So these are before notched points came along about 7,000 years ago. And we started seeing these on the landscape out here, dating on average between 7,000 [years] and about 15,000 years ago. So there’s lots of these points present on this landscape and they are time markers all by themselves.
Miller: So that was your assumption, sometime between 7,000 and 15,000 years ago. But obviously, we’re talking now because what you found turns out to be thousands of years older. Can you tell us about the layer of volcanic ash that was on top of some of the things that you eventually found?
O’Grady: Yes. When we were excavating here, we did a test excavation in 2011 and the other one in 2012 along with a field school. And what we found was that there was a layer of rock that looked like it might have been protecting an ancient surface. So we got somebody out here who could break up this rock layer that appeared to be from a collapse of the Rockshelter as some time passed. And when we got underneath those rocks, we got into a layer, a deposit of sedimentary material that was protected.
During the first part of that excavation, as we broke through the rocks, we found a layer of volcanic ash that we thought was Mazama from the eruption that formed Crater Lake 7,600 years ago. And Mazama is always a great thing to see because then you’re dealing with a site that’s at least 7,600 years old. And then that winter when we sent that material off to Washington State University, they identified it as a very clean sample of Mount Saint Helens SG Tephra, or volcanic ash, that dates at the most recent about 15,000 years in age.
So right then we are realizing that we have a volcanic layer of ash that’s twice as old as we expected it to be, and anything else that was underneath it, if it was in the proper orderly association that we expect with stratigraphy, should be older than that volcanic ash.
Miller: And in fact, that’s what radiocarbon dating has confirmed, most recently just this past year. Two different sets of things that you have found - tooth fragments from, I guess now extinct animals, and some human tools. Can you tell us about the tooth fragments first?
O’Grady: Yes. After we got through that volcanic ash layer, we found a concentration of, I think there were 27 or 28 fragments of tooth enamel. One of the pieces was so large that it fit across the palm of my hand and it was clearly from an animal that didn’t exist on the landscape in modern times. And so that by itself was really exciting, but we didn’t know what it was.
That winter when we were out of the field and back in at the university, I took it over to Edward Davis, who is a paleontologist-geologist at the Condon Collection for the Museum of Natural and Cultural History. He and I compared that to fossils from the Juntura formation and found that it matched very nicely with a camel mandible that was excavated at some time in the past. So comparing that visually, it appeared to be camel.
Miller: So 18 or so thousand years ago, camels were roaming around what’s now near Burns?
O’Grady: Yes, there were actually quite a few of them scattered across North America and we believe this to be what’s called Yesterday’s Camel.
Miller: And there was the other piece, I understand was from a variety of bison which also is no longer with us.
O’Grady: That’s what we believe that piece to be. It was in the same concentration of tooth enamel, but it appears to be a bison tooth and we’re trying to verify that right now through other means.
Miller: What can you tell us about the orange agate tools, scrapers it seems, that were also found?
O’Grady: So, according to superposition, or looking at sediments in the ground in the natural order of things, the oldest material should be at the bottom or beneath the more recent material. So we were looking at the volcanic ash and then underneath that we found the camel tooth enamel, and then 10 centimeters below the tooth enamel we found an orange chalcedony, or what looks like a very bright colored agate tool, but agate is banded, chalcedony is unbanded and translucent. So there’s a bit of a difference between those two.
Miller: What might the tool have been used for?
O’Grady: It has multiple edges. And so when you take a look at it, it has one convex edge so it’s kind of a curved cutting edge. One side has a flat edge that appears to be another type of cutting edge or maybe a scraper. And then another side of it is not quite square but more rectangular, but the third side has flakes taken off on opposite sides to form a sawtooth edge. And that edge has been used so much that the teeth on it are polished almost round.
Miller: So it’s a kind of multi tool. You could do different things with it depending on which edge you had.
O’Grady: Yeah, it’s like an early Swiss army knife.
Miller: So when you add this all up with the added detail that you got a kind of second confirmation of the dating, putting this at least 18,000 years ago, what’s the significance of that finding? What does it mean to you that humans were there more than 18,000 years ago?
O’Grady: Our first radiocarbon date on the camel tooth enamel fragment was done by Tom Stafford, who’s one of the leaders in the world in preparing samples for AMS radiocarbon dating. So you can take a tiny amount of material and date that very accurately using the radiocarbon method. And so we got that first date in 2018 and it came back in the 18,300 year time range.
And it was just scary because having a single date of material that is that old suggests that we may have a very old site here. And so the first thing we want to do is re-date that same sample plus add an additional sample to verify that those dates are likely correct.
Miller: The word you used there is scary. You didn’t say it was exciting. What was scary about it?
O’Grady: Oh, well, it’s both exciting and scary, but the scary part is that a single date is not something that you use to support an idea of the age of a site, you have to verify that that date is correct. And so we were sitting looking at a date of 18,000 years and beyond and trying to determine how accurate that was, so we needed to get additional dates. And that was the scary part, is that you don’t want to announce something like that, that’s that old without having something to back it up.
Miller: Which you then did get that second confirmation this year in 2023, which is why we’re talking now. So what does it mean that humans were there, to the best of our scientific understanding now, that long ago?
O’Grady: Well, there’s a couple of things. So the fact that we have the radiocarbon dates on these tooth enamel fragments and they’re above where that stone tool came from suggests that perhaps the stone tool is even older than the dated camel tooth enamel. So that’s a highly significant thing.
And then the other thing about it is just that it’s pushing back the idea of how old sites can be in North America. And that we have evidence of extinct animal species in association with stone tools. So that’s something that is hard to come by, and to have them at the transition from the Pleistocene or the Ice Age into more modern conditions, even though that took a long time, means that we are stretching the timeline for humans in Oregon and points beyond further back. And there are other sites that are old, that are close to that age and some that are perhaps older through North and South America. But these are very strong dates.
Miller: Does this change the most accepted theory of how and when humans arrived in the Americas?
O’Grady: I think that has been in flux for quite a while now. So for years, since the 1930′s, the idea has been among archaeologists and conveyed to the public, that there is a certain type of stone tool called the Clovis point. And those are found in association with Ice Age animals, and they date between about 12,800 and 13,300 years in age. So those Clovis points were thought to be the first in North America and it was hard to break through that barrier in thinking until we started finding older sites. Another university site called Paisley Caves was dug by Dennis Jenkins, and his team identified material at that cave that was 14,300 years in age and started breaking down that barrier. There were other dates that were coming out about the same time and we’re slowly pushing the timeline back. You know, honestly, I don’t know - for now, this is an old date, but in another day or another week there may be older dates that push the timeline further back.
Miller: I guess you can enjoy the designation while you have it. Pat O’Grady... Sorry?
O’Grady: Go ahead.
Miller: Oh, I was going to thank you, but I wanted to give you a chance to give us a final thought.
O’Grady: Oh, just the final thought is that it’s a relief to see these dates match up because now we can start talking about this site in terms of what the basement age of the site is and start putting out the papers we’ve been waiting to until we had that verification.
Miller: Pat O’Grady, thanks very much for your time.
O’Grady: Thank you.
Miller: Pat O’Grady is a staff archaeologist at the University of Oregon’s Museum of Natural and Cultural History.
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