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Researchers get some clarity on Chaco Canyon's 1,000-year-old supply chain mystery

A crow sits on top of a brown ancient stone wall at Chaco Culture National Historical Park.
Rae Solomon
A crow sits atop a wall at Chaco Culture National Historical Park on Dec. 26, 2014. Over hundreds of years, ancient ancestral Puebloans hauled massive amounts of heavy building materials to the site from up to 60 miles away. Researchers at CU Boulder have tested out a new theory about how the Puebloans accomplished that feat.

Researchers at the University of Colorado Boulder may have solved a 1,000-year-old supply chain mystery: How did ancient ancestral Puebloans transport heavy building materials to Chaco Canyon, one of the Southwest’s most important archaeological sites?

Chaco Canyon was a hugeancestral Puebloan city located in what is now Northern New Mexico, about 100 miles south of Durango. Its massive stone and timber buildings were constructed starting in 800 A.D. with materials taken from as far away as the Zuni Mountains to the south and the Chuska Mountains to the west. Archaeologists have long been puzzled as to how the ancestral Puebloans managed to carry those heavy building materials that far - as much 60 miles away.

For years, archaeologists believed that the 16-foot-long timbers transported long distances to Chaco Canyon weighed about 600 pounds.

That astonished CU Boulder Integrative Physiology Professor Rodger Kram.

“As a person who studies biomechanics and physiology of the human body, I was like, that's crazy,” Kram said. “I don't know how they could have possibly done that.”

That astonishment was Kram’s entry point into the mystery. His first move was to revise the inaccurate 600 pound weight estimate by doing his own weight estimations on a log from his wood pile.

“I cut a section that was one foot long and I weighed it on my bathroom scale. The average logs that were carried to build these great houses at Chaco were about 16 feet long, so I multiplied it by 16,” he said.

Kram rewrote history when he published apaper showing the Chaco logs were actually much lighter, weighing closer to 200 pounds. That still left a bigger question unanswered, though.

“It's still not a piece of cake to haul a 200 pound log 60 miles,” Kram said.

So how did the ancestral Puebloans manage it? Kram hypothesized that they pulled it off with tumplines – straps that allow freight to be suspended from the top of the head, making it physiologically easier to lug heavy loads.

“Once you get it positioned so that it's right on the crown of your head, then the load lines up with your neck and with the rest of your spine,” Kram said.

When a load is positioned at the top of the head, the spine supports the weight and it doesn’t fatigue muscles.

“It feels a little weird to have something pressing on your head for hours on hours, but it doesn't do any real damage,” he said.

An ancient brown wall with small square windows at Chaco Culture National Historical Park
Rae Solomon
A wall at Chaco Culture National Historical Park, Dec. 26, 2014. Over 200,000 large, heavy timbers were hauled to the site from dozens of miles away to lend structural support to buildings constructed there. One piece of ancient timber is visible in this photo as a beam supporting the stones above a keyhole opening.

Tumplines are hardly a new innovation. They have been used by many cultures across the world for thousands of years, from African to Asia and the Americas. Kram’s big insight was that multiple tumplines could have been attached, side by side, to a single log, allowing several people to share the load. The roads around Chaco Canyon would have been wide enough to accommodate a line of people walking next to each other in a row - an ideal setup for Kram's multi-person tumpline theory.

Kram decided to take proving his theory a step—or haul—further, though.

“You can convince people if you show that something is actually feasible," Kram said. "Maybe the best way is to do it yourself.”

Kram and a fellow researcher decided to test out the theorized method in the foothills outside of Boulder. They used a log that weighed 132 pound. Each attached a tumpline to one end of that log to share the load.

“The actual demonstration was to try and walk a long distance carrying 66 pounds per person, walking side by side,” Kram said. “We chose a forest road up here in the foothills and outside of Nederland and we walked up and down this darn road. That's five miles round trip.”

The two made three round trips over the course of the day.

“Everybody else who was hiking there scratched their head and asked us what the heck we were doing,” Kram recalled. “It was a long, hard day.”

It proved worthwhile, though, because their efforts helped prove that the multiple-tumpline method was viable.

“We calculate that probably each of the big timbers took three people and took them about four days to get from where the trees were cut down to where they were used for the construction site,” Kram said.

Kram’s experiment isn’t definitive proof that ancestral Puebloans used to haul their loads, but Kram says his research suggests that that's likely what happened.

“It fits with all the evidence: they used tumplines, they made the roads very wide,” Kram said. “It's probably more than feasible. It's likely the best way to do it.”

Kram said the next step is to do more experimental work - this time, on location at Chaco Canyon, where they can demonstrate the tumpline method works as they trace the ancient hauling routes of the ancestral Puebloans.

I am the Rural and Small Communities Reporter at KUNC. That means my focus is building relationships and telling stories from under-covered pockets of Colorado.
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