North American Database of Archaeological Geophysics
North American Database of Archaeological Geophysics
Abstract/Summary:
Project Name: Geophysical Investigations South of Mound 48
Reference: DeVore, Steven L., Aaron Fogel and Kelsey Lowe (2003) Geophysical Investigations of the Area South of Mound 48, Cahokia Mounds State Historic Site, St. Clair County, Illinois. National Park Service, Midwest Archaeological Center Lincoln, Nebraska.
During the week preceeding the FY2003 Archaeological Prospection workshop at Cahokia Mounds State Historic Site, personnel from the Midwest Archaeological Center and Minnesota State University-Moorhead, conducted geophysical investigations in an area south of Mound 48. The investigations were conducted as a training exercise and to help the park staff and researchers identify the location of the West Palisade line near the mound. Magnetic gradient surveys with the Geometrics cesium gradiometer and the Geoscan Research fluxgate gradiometer were conducted in a 20 m by 80 m area. Resistance survey of the grid was conducted with the Geoscan Research resistance meter, multiprobe array and multiplexer set to take three depth readings at each survey point. A conductivity survey of the same area was conducted with the Geonics EM38 conductivity meter, as well. Disturbed areas were noted in the four data sets. The magnetic gradient and conductivity data identified the locations of iron/steel artifacts. A linear anomaly in the conductivity and resistivity data sets may represent the location of the West Palisade line. While several magnetic and conductivity anomalies are probably related to modern urban related activities of the previous landowners, residents, and visitors, other magnetic, conductivity, and resistivity anomalies may be associated with the Mississippian occupation of Cahokia. In addition, two vertical electrical soundings were conducted before and during the workshop. The one at Mound 48 indicates the presence of highly resistive sands while the one at the Northeast Palisade line suggested a four layer curve comprised of clays that are more conductive and loams.