GEOPHYSICAL SURVEYING ON THE SOUTHERN TERRACE OF CAHOKIA'S MONKS MOUND

The Cahokia Mounds State Historic Site is located within the Mississippi River Valley approximately 12 kilometers east of Saint Louis, Missouri in the expansive alluvial floodplain known as the American Bottom. The ancient city, today known as Cahokia, is the site of the rise and fall of the largest and most complex Native American society in North America. Monks Mound, a large platform pyramidal mound, and the largest man made earthen structure north of central Mexico, served as the religious, political, and social center of Cahokia. Three geophysical methods, including electrical resistivity, electromagnetic conductivity, and magnetics, were used to conduct surveys on the eastern half of the Southern Terrace of Monks Mound to search for evidence for human occupation. The geophysical results presented as contour maps and profiles reveal numerous anomalies having strong correlations among the different datasets. The positive correlation of the anomalies increases their potential for archaeological significance. The resistivity anomalies are subtle and broader than the corresponding conductivity and magnetic anomalies. The magnetic anomalies are more isolated from the background and show more detail and better definition. The results demonstrate the complementary nature of the data and its usefulness in locating potential excavation sites, as well as giving rough estimates of the depth range and physical properties of the sources.