Some of the Chaco Canyon ruins are still standing

Puebloans in Treeless Chaco Canyon Hauled 240,000 Trees over 75 KM for House Construction

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Analysis of tree-ring patterns shows the prehistoric Pueblo Indians who built the multi-story great houses in Chaco Canyon, New Mexico, at one time hauled huge wooden beams a good distance from one valley for their construction and then suddenly switched to another valley’s trees. Archaeologists doing the research said both mountain ranges are about 75 kilometers (46 miles) from Chaco Canyon, which was virtually treeless.

The researchers said over the years there has been intense debate over the source of the trees used as beams in the wood-and-stone structures as there were seven nearby mountain ranges from which the trees could have originated. Some of the structures have hundreds of rooms and stand five stories high. They are among the largest buildings dating to before 1492 in North America.

The builders of the great houses at the iconic site used thousands of trees to do the construction between 850 and 1140 AD, says an article in Phys.org about the research. Painstaking analysis of the wood was conducted by University of Arizona Laboratory of Tree-Ring Research.

Christopher Guiterman, the lead author of the paper ( abstract) in the Proceedings of the National Academy of Sciences, said his team used the dendroprovenance method of determining where the trees for supporting beams originated. This method had not been used in the American Southwest before his study.

Wooden beams for Chaco Canyon’s great houses came from two different valleys, researchers said.

Wooden beams for Chaco Canyon’s great houses came from two different valleys, researchers said. (Photo by Stephen C. Price/ Wikimedia Commons )

Previously, other University of Arizona researchers’ chemical analysis of the wood showed one source as the Chuska Mountains. But Guiterman et al.’s research shows another, earlier source was wood from the Zuni Mountains. About 70 percent of the wood in the great houses came from those two valleys.

For four years, Guiterman and colleagues looked through some 6,000 wood specimens collected from Chaco Canyon great houses and nearby areas. The specimens are stored in many boxes at the Laboratory of Tree-Ring Research, Phys.org says. Researchers began collecting wood from the pueblos and nearby areas in the 1920s.

A drawing showing construction of the Chaco Canyon great houses

A drawing showing construction of the Chaco Canyon great houses (Drawing by Stephen H. Lekson/ Wikimedia Commons )

Mr. Guiterman compared the ring patterns on the beams from 170 great houses to trees from seven surrounding mountain ranges.

"The casual observer will see hundreds and hundreds and hundreds of beams sticking out of the walls. There's wood all over the place in these structures," Mr. Guiterman told Phys.org. "They're built out of stone and wood."

The abstract sums up in PNAS the basis of the research:

“The iconic great houses of Chaco Canyon occupy a nearly treeless landscape and yet were some of the largest pre-Columbian structures in North America. This incongruity has sparked persistent debate over the origins of more than 240,000 trees used in construction. We used tree-ring methods for determining timber origins for the first time to our knowledge in the southwestern United States and show that 70% of timbers likely originated over 75 km from Chaco. We found that a previously unrecognized timber source, the Zuni Mountains, supplied construction beams as early as the 850s in the Common Era. Further, we elucidate shifting dynamics of procurement that highlight the importance of a single landscape, the Chuska Mountains, in the florescence [height] of the Chacoan system [around 1060 AD].”

The change in the source of wood coincides with a change in construction styles and activity. The builders changed their masonry style, and then the amount of construction increased greatly, said Mr. Guiterman, a doctoral candidate at the University of Arizona’s School of Natural Resources and the Environment.

Chaco Canyon structures were built with wood mainly from two valleys, both about 46 miles from the city center that served as a hub for trade, politics and religion.

Chaco Canyon structures were built with wood mainly from two valleys, both about 46 miles from the city center that served as a hub for trade, politics and religion. (U.S. National Park Service photo/ Wikimedia Commons )

Also, around the same time other people’s projectile points, carving tools and pottery started coming to Chaco Canyon from the Chuska Mountains, Mr. Guiterman told Phys.org.

The Chaco Culture sites are on UNESCO’s World Heritage Site list. UNESCO says the Pueblo people lived in a vast area of the Southwestern United States, including Chaco Canyon, from 850 to 1250. Chaco Canyon itself was a hub of political, trade and ceremonial activity.

“Chaco is remarkable for its monumental public and ceremonial buildings and its distinctive architecture – it has an ancient urban ceremonial centre that is unlike anything constructed before or since,” the UNESCO article says.

Feature image: Some of the Chaco Canyon ruins are still standing (Photo by HJPD/ Wikimedia Commons )

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