Analyzing and Presenting Resistivity Data from Emerald Mound Archeology Site in Attempt to Discover a Mississippian Trail

The ancient city of Cahokia, located in southwest Illinois, was the largest Native American community north of modern-day Mexico and was best known for the large, mound like structures they built. Emerald Mound is considered to be a part of this ancient Mississippian culture and is located to the east of Cahokia. In a 1940 aerial image of Emerald Mound, there are two linear, parallel features resembling paths or roads that extend southeast from the mounds. These features cut across two modern roads and multiple farm fields but are no longer visible in today’s aerial images or orthophotographs, likely due to modern agricultural modifications of the landscape. Understanding the travel techniques of these ancient civilizations can help us further understand their culture. However, visual analysis alone is insufficient to establish whether these features were indeed produced by human travel. In addition, other undiscovered roads may exist beneath today’s fields. In this study, we tested electrical resistivity to see whether the method can detect these now-hidden features. Years of travel on a path would compress the soil beneath the theorized path and in an attempt to measure this, 10 resistivity lines were constructed perpendicular to the linear features. We measured resistivity at multiple depths (from 0.26 to 2.14 meters below the surface) along the 10 transects. Each profile was about 150 meters long and spaced approximately 100 meters apart. Most resistivity profiles showed higher resistivity in two regions: 40-50m and 110-120m from the south end, corresponding approximately to the location of the linear features. This pattern was consistent through multiple different profiles and depths, but was not detected in all profiles or depths. Despite limitations due to the signal:noise ratio in the data, the relative continuity of high resistivity values suggests that the linear feature was likely produced by this ancient civilization and is not a by-product of modern agriculture.