A study led by Dartmouth using multi-sensor drones revealed a major circular earth action in what may have been the Etzanoa, an archaeological site near Wichita, Kansas. Archaeologists speculate that the site was visited by a Spanish expedition, led by Juan de Onate, the controversial conqueror, in 1601. The earthworks may be remnants of the so-called “Council Circle,” because they resemble many other circular earthworks in the area, according to Results of the study published in American Antiquity.

“Our findings show that massive, undiscovered earthworks may still be found on the Great Plains. You just need a different archaeological approach to identify them,” said lead author, Jesse J. Casana, professor and chair of anthropology at Dartmouth. He added, “Our results are promising in indicating that there may be many other remarkable monuments that have yet to be documented, if we look seriously enough.”

Monuments have different thermal effects. After the Earth cools at night, things underground cool and emit heat at different rates, allowing researchers to define features based on thermal infrared radiation. Researchers acquired thermal and multi-spectral imagery of the site using drones.

The area is 18 hectares Location The drone survey is currently home to a farm in the Lower Walnut River Valley, which is being used as a pasture. Topographically, the area is flat and there are no visible archaeological features. However, the photos show that there is an ancient, circular crater underground, 50 meters wide and about 2 meters thick, that has been filled in. When the soil erodes, it fills the trench with a different type of soil than it was before, thus it retains the water differently giving it unique thermal properties. Water retention levels also affect vegetation. Using near-infrared images, the researchers were able to pinpoint the areas that were filled with because the lawn growth was more active. As the study suggests, the results provide evidence of what might have been a “single sprawling population center” of its day.

To ensure that the results were not anomalous, the team compiled a time series of aerial and satellite images of the area from the US Department of Agriculture and other federal agencies. They found that the circular element was “poorly visible in June 2015 and July 2017 but not in June 2012 or February 2017.”

Debate is widespread about what council circles were used, whether they are of an astronomical nature or made for ceremonial, political and / or defensive purposes. “While we may never know the purpose or significance of using the council’s circles, new archaeological methods allow us to see that people did these excavations,” Cassana added.