UNM Professor of Anthropology Wirt H. Wills, and two former graduate students, Brandon L. Drake and Wetherbee B. Dorshow, have authored a paper released by the Proceeding of the National Academy of Sciences today that challenges the notion that the Ancestral Puebloan society that thrived between 860 and 1140 A.D. in Chaco Canyon collapsed as a result of deforestation.

The paper, ”Prehistoric Deforestation in Chaco Canyon?," argues that there is no real physical evidence that Chaco Canyon ever had forests in the immediate vicinity of the canyon – so it’s impossible to say that deforestation occurred. Papers that theorized the presence of local woodlands relied heavily on an absence of evidence. Two packrat midden samples from the Bonito phase of the canyon did not have macro botanicals from Ponderosa pines in them so researchers theorized that there was an absence of pines in the immediate area.

The paper also points out technical problems with using strontium isotopes to identify sources of timber used in Chaco construction. Wills, Drake and Dorshow demonstrate that the results of research to identify the location of the trees used could not clearly distinguish between wood that might have been harvested in the canyon and wood that might have been found in mountainous areas in the general vicinity.

The problem is that “we just don’t know,” Wills said. Wills is co-leader of a UNM research team that has worked for the past decade at Chaco Canyon trying to unravel the mystery of what caused a civilization to thrive at one point in time, then slowly wither and disperse. Wills says they have many more questions than answers.

His research group is searching now for agricultural fields that might have existed during the Bonito phase.  “We don’t know for example whether the people who lived in the canyon were able to grow enough maize to support their communities or whether they had to import some or much of their food.”  The fields he seeks may lie deeply under clay that now covers much of the canyon floor. These clay deposits were laid down by flooding from sources outside the canyon and now largely obscure the places where Chaco farmers cultivated crops. 

A partial re-excavation by UNM archaeologists of a trench dug during the 1920s has uncovered canals that appear to have been used to reroute rapidly flowing water around a Pueblo Bonito structure. “We know where the water came from, but we need to understand where it was going. Was the water diverted to fields or reservoirs, or simply away from people’s homes,” Wills said.

Wills says there is a mountain of research still to be done in this canyon, a lifetime of work for students who want to answer complex questions. He says the unknowns are enormous and the list of possible research questions is long.

  • Are there other isotopes besides strontium that might give a clearer picture of where the wood used in the canyon structures came from?
  • Did the availability and sources of water change through time?
  • How productive was farming in the canyon?
  • What did it look like, large fields or small?
  • How important was irrigation?

Finding answers to those questions make research at Chaco Canyon a continual process of discovery. He says there was a reason or reasons that the people who built the great structures at Chaco moved away, but so far there is no compelling answer in the archeological record about what that was.

For more about what Wills and other UNM researchers are finding out about the people of Chaco Canyon, below is a recent list of research.

On the Trail of the Lonesome Pine:Archaeological Paradigms and the Chaco “Tree of Life”

Strontium Isotopes and the Reconstruction of the Chaco Regional system: Evaluating Uncertainty with Bayesian Mixing Models

Modeling agricultural potential in Chaco Canyon during the Bonito phase: a predictive geospatial approach

The 5.1 ka aridization event, expansion of pinon-juniper woodlands, and the introduction of maize (ZEA mays) in the American Southwest

Agriculture and community in Chaco Canyon: Revisiting Pueblo Alto