Mysterious Pueblo Society Built Huge Chaco Canyon City With Only Their Heads

Around 1000 years ago, Chaco Canyon in northwestern New Mexico was home to tens of thousands of members of an ancient Native American culture known as the Anasazi – a name given to them by the Navajo which means "ancient enemies." Today their descendants prefer them to be known as Ancestral Puebloans whose territory covers what is now referred to as the Four Corners region of the United States where Utah, Arizona, New Mexico and Colorado meet. Three mysteries surround the Ancestral Puebloans – who they descended from prior to 850 CE, where they disappeared to after 1200 CE, and how they built what we now call  “Great Houses” – structures made from timber and stone which rose up to four stories high and contained hundreds of rooms. A new study has solved the third mystery – how they carry as many as 200,000 16-foot-long wooden beams to Chaco Canyon from forests over 60 miles away. As the title states - they used their heads … but not just by thinking about it.

“Researchers have proposed various load-carriage methods, speculated about how many porters would be needed and their speed of transport, but none have conducted empirical investigations.”

In 2020, during the summer of the COVID pandemic lockdown, Rodger Kram, an associate professor emeritus of integrative physiology at the University of Colorado Boulder, and James Wilson, an undergraduate then studying biochemistry at the school, decided to tackle the Chaco Canyon mystery that had stumped other researchers. The city of “Great Houses” was impressive in its heyday – fifteen of the structures were the largest buildings ever built in North America until the 19th century. Many of the smaller buildings appeared to be lined up with solar and lunar cycles, requiring knowledge of astronomy and precise construction techniques. While their stone quarries were close to the canyon, the nearest timber forests were not. Rodger Kram was already interested in Chaco Canyon when the pandemic hit, and he used the time to do deeper research into the building of the city. One aspect that baffled him was the massive weight of the timbers used for roof beams – most estimates put them at around 600 pounds (275 kg). Kram thought that was an impossible for humans living in 850 CE to move and came up with a ‘lockdown’ way to prove it.

“I cut a 1-foot-long section of pine and weighed it on my bathroom scale. I multiplied by 16 feet and realized, ‘That can’t add up to 275 kilograms.’”

As he explains in their study, published in Journal of Archaeological Science: Reports, and in a UC Boulder press release, Kram and Wilson studied dried wood and came up with a new estimate - a pine log measuring about 16 feet long should weigh about 187 pounds (85 kg). In their lockdown-crazed minds, that seemed like a weight two guys living in Colorado who missed being outside could carry. They found a log about the right size and tried carrying it on their shoulders. That worked for a few feet but not 60 miles.  Having time on their hands, they then researched log carrying techniques and found one used by sherpas in Nepal – tumplines. Sherpas were (and still are) known to be able to carry large loads up mountains using tumplines … which are simply straps worn around their heads. The pair learned that this tumpline technique allowed sherpas to use the bones of their necks and spines to bear the weight, rather than just their muscles. They know what you’re thinking … really?

“I had Dr. Kram and James initially focus on walking greater and greater distances with what felt like light tumpline training loads. As they became more comfortable with their training, we began alternating training days between carrying light loads for greater distances and heavier loads for shorter distances.”

The team added a third member - Joseph Carzoli, a study co-author and certified strength and conditioning coach who got his doctorate in integrative physiology from CU Boulder. Carzoli had the men train slowly and build up their strength, endurance and mileage over a three month period of using tumplines to carry increasingly heavier loads six to seven days a week. It’s hard to believe they didn’t go crazy from an earworm like The Beatles’ “Carry That Weight,” but they eventually were ready for a real log.

“Two authors trained themselves to use tumplines and together carried a 60 kg timber 25 km with the timber oriented transverse to the walking direction. Total elapsed time was <10 h and walking speed averaged 4.5 km/hr. Individual walking speed with a 30 kg tumpline load was only ∼10 % slower than the preferred unladen walking speed.”

Carzol took  Kram and Wilson to a forest road going to Gross Reservoir southwest of Boulder and loaded them up with a 60 kg (132 pound) timber. Each man had a tumpline on his head with the other end wrapped around one end of the log. They carried the log suspended between them on their backs where a backpack would be positioned and managed to hit just under 3 mph, which is slightly slower than their normal walking speed. (See a photo of the tumpline and the men here.) When they needed to rest, they used “tokmas” (see a picture here) – T-shaped supports used by Nepalese sherpas to hold the their loads without lowering them to the ground. They managed to walk comfortably with the only stress coming from the strap of the tumpline rubbing their heads. The study concludes that they have solved the mystery of the building of the Ancestral Puebloans’ Great Houses:

“Timber transport to Chaco using tumplines is clearly feasible. We close by considering the implications of tumpline timber transport on the socio-political dynamics of Chacoan society.”

The researchers proved that carrying 200,000 timbers 60 miles to Chaco Canyon “may not have been as back-breaking” as once thought ... as long as you have tens of thousands of people helping. If that was the case, why did they stop around 1200 and abandon the houses and the canyon? It is speculated that the tumplines were too efficient and the Ancestral Puebloans decimated the forests. Also, they had help from climate change … a 50-year drought began around 1130 and helped wipe out their sources of timbers. In their new locations, they became the Pueblo Peoples of New Mexico and the Hopi of Arizona.

Anasazi may have meant "ancient enemies," but it looks like they were the enemies of the trees, not just the Navajo. In the end, the Ancestral Puebloans should have used their heads for thinking about the timbers instead of just carrying them.