New studies from University of Colorado offer different version of Chaco Canyon's past

Research points to much-smaller full-time population

Mike Easterling
Farmington Daily Times

FARMINGTON — New research from a team headed by a University of Colorado scientist casts doubt on Chaco Canyon's status as a significant year-round population center during the Anasazi era.

Larry Benson, an adjunct curator at the CU Museum of Natural History, as well as a hydrologist and geochemist, led a team of researchers that published its findings about the settlement's food sources in the November 2019 edition of the Journal of Archaeological Science, a monthly, peer-reviewed academic journal.

Additionally, Benson maintains there is reason to believe Chaco was home to only a small, "caretaker" population on a year-round basis, filling up only occasionally for large ceremonial events that required large amounts of food to be imported.

The research largely confirms what Benson thought when he got his first look at Chaco Canyon — now known as Chaco Culture National Historic Park — decades ago.  As a native Midwesterner who had grown up amid lush corn fields, he didn't see any way that the arid territory surrounding the settlement could produce maize or other crops in significant amounts – and certainly not enough to feed the 2,300 people often cited as the population of Chaco during that era.

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Pueblo Bonito is pictured April 14, 2019, at Chaco Culture National Historical Park.

During a telephone interview on Jan. 10 from Boulder, Colorado, Benson said the research focusing on Chaco's unsuitability for large-scale agriculture that was featured in the Journal of Archaeological Science paper didn't break a lot of new ground, as much of it had been published before. But it did go into much greater detail, crunching large amounts of data that strongly support the idea that the area could produce only enough food on its own to sustain a very small population.

Only a minimal amount of maize could have been grown at Chaco because of its aridity, short growing season and the flooding of the valley floor that occurred frequently in the summer, Benson writes with his fellow authors, Deanna Grimstead, John Stein, David Roth and Terry Plowman.

Benson said it was clear to him that dryland farming was not a feasible option for Chaco residents during the prehistoric era, and he said there is no physical evidence that irrigation took place in the valley on a large scale.

"It would have taken a monumental ditch and berm system to prevent (summer monsoon) flooding and direct the flow of that water," Benson said.

If such a system had been built, he said, "You should be able to see it now, and you can't, so my position is, they didn't."

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The entrance to Chaco Culture National Historical Park is pictured April 14, 2019, with Fajada Butte in the background.

According to Benson's research, even if Chaco residents had farmed 100 percent of the valley floor and the surrounding side valleys — a dubious proposition, he noted, estimating that only around 20 percent of that land is actually usable for agriculture — it could have supported a population of 1,000 people at most.

Additionally, the authors also write that 2,300 residents and their need for meat quickly would have eliminated the small and large animal populations, such as deer and rabbits, in the valley.

"That protein wouldn't even have lasted a year at Chaco for 2,000 people," he said.

The implication is clear, according to their research – that meat and maize were carried into the valley by porters from outlying areas to feed Chaco's residential population. The research indicates that the primary source of that food was the Chuska Slope, the eastern slope of the Chuska Mountains directly west of Chaco.

To meet the nutritional needs of a full-time population of 2,300 people, porters carrying that food faced an enormous task, according to the paper. They would have needed to make 18,000 trips a year to the canyon while burdened by a load of 45 kg — the equivalent of nearly 100 pounds. An average of 50 porters a day, each traveling from a minimum distance of approximately 37 miles and sometimes  much farther, would have had to enter Chaco to keep the population fed, according to the research.

That is where Benson's research for the Journal of Archaeological Science article ended. He subsequently authored another paper — which he said he is having trouble getting peer reviewed, much less published — in which he suggests that Chaco's year-round population was much smaller than is generally believed.

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Pueblo Bonito is pictured April 14, 2019, at Chaco Culture National Historical Park.

Benson bases that argument partly on analyses of Chaco's burial sites. Though he acknowledges that not every body buried in the valley has been located, he said the relatively small number of graves that have been located do not support the typical third-world death rate for a population of approximately 2,300 people. The number of graves more closely aligns with that of a population of a few hundred, he said.

Benson described his most recent paper as a hypothesis and said no one seems to like it. But he said his research indicates to him that Chaco most likely was home to a small caretaker population on a year-round basis, and a large number of pilgrims came to visit the settlement from outlying areas only for ceremonial events.

Furthermore, he said, it indicates that Anasazi elites did not live in Chaco's greathouses — another long-held belief — and instead lived on the periphery of the San Juan Basin, where they controlled the production of food resources and solidified their power.

Benson acknowledged those ideas present an "alternate reality" of what went on at Chaco, but he declined to characterize them as revolutionary.

"I think people have proposed parts of these ideas all along," he said. "What's different is I've done the calculations and (gathered the data)."

Mike Easterling can be reached at 505-564-4610, or via email at