These scientists carried logs on their heads to solve the mystery of Chaco Canyon End-shutdown

Enlarge / Rodger Kram, left, and James Wilson carry a tufted log with Boulder Foothills in the background.

Patrick Campbell/CU Boulder

The so-called “big houses” of Chaco Canyon in New Mexico it may have taken decades or more to build. Most of the large complexes had four or five stories and an average of more than 200 rooms, with the largest having up to 700 rooms. The complexes also featured large circular ceremonial areas called kivas. To build these great houses, archaeologists have estimated that the Chacoans would have needed wood from some 200,000 trees, and those 16-foot-long wooden beams must have been transported from mountain ranges up to 70 miles (110 km) away.

Many scientists have hypothesized how the Chaco could have accomplished this feat. The latest theory is that the Chacoans may have used simple devices called stumblingstill favored by the Sherpas in Nepal, according to a new paper published in the Journal of Archaeological Science: Reports. To test that hypothesis, co-authors Rodger Kram and James Wilson spent the summer of 2020 training until they could haul a heavy log about 15 miles using bundles. “Some people baked sourdough bread during COVID,” Kram said, Professor Emeritus of Integrative Physiology at the University of Colorado at Boulder. “Instead, we would carry sand and heavy logs using our heads.”

There are no preserved wood scrape marks near the site, and the people of Chaco Canyon had no draft animals or even wheels, according to Kram and his co-authors. So the logs must have been carried by people, most likely along the wide paths that linked this world. A 1925 publication featured a photograph showing eight Zuni Pueblo youths carrying a log: four on each side holding slender cross poles at hip height, with the log positioned on top. That photograph influenced many of the mechanisms proposed for transporting the logs. things though et al. noted that there is no clear evidence that Zuni Pueblo residents share cultural connections with the people who once inhabited Chaco Canyon. “We feel it is doubtful to infer Chaco-era timber transport methods from a 20th-century staged image,” she wrote.

Others have suggested that the beams were rolled rather than carried to construction sites, perhaps bundled into smaller pieces of wood for protection or carried on shoulders. And the oral traditions and published ethnography of the Pueblo and Dineo peoples descended from the Chachoanos do not shed much light on the subject either. There is an account that the beams for Pueblo Bonita were transported in small carts made from a small tree, with a cross section at each end that served as a rudimentary wheel. But that account is inconsistent with the known origin of the woods (the Chuska mountains, Zuni, San Mateo, La Plata, ad Sa Juan) and there is also no archaeological evidence of the existence of such carts, according to the authors.

The ruins of Chetro Ketl in Chaco Canyon, with the large kiva of the complex.
Enlarge / The ruins of Chetro Ketl in Chaco Canyon, with the large kiva of the complex.

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Kram developed his own theory of how the Chacoans accomplished the feat, beginning with his realization a few years ago that assumptions since the 1980s about the mass of a typical roof beam (beam) used in one of the big houses was probably too tall: 275 kilograms, a little over 600 pounds. “I cut a 1 foot long section of pine and weighed it on my bathroom scale,” Kram said. “I multiplied by 16 feet and realized, ‘That can’t add up to 275 kilograms.’”

He and Wilson, then a biochemistry student at the University of Colorado, Boulder, read about the properties of dry wood and published their conclusions Last year they calculated that a 16-foot-long pine log weighed more than 85 kilograms, or just over 185 pounds. That changed the calculation significantly when determining how many people would have been needed to transport the logs 60 to 70 miles. And they decided to test themselves if the trip was possible.

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