North American Database of Archaeological Geophysics
North American Database of Archaeological Geophysics
Abstract/Summary:
Project Name: La Ciudad, AZ;
Reference: Bevan, B.W. (1983). Electromagnetics for Mapping Buried Earth Features. Journal of Field Archaeology 10(1):47-54. Reproduced from Journal of Field Archaeology with the permission of the Trustees of Boston University. All rights reserved.
Electromagnetic surveys are fast method of locating and mapping some large earth features such as leveled mounds and refilled ditches. They can be a substitute for resistivity surveys and are particularly suitable where the surface soil is dry, hard, or rocky, or where the vegetation is moderately dense. As in all geophysical techniques, it is necessary that the features to be located are sufficiently different from the surrounding terrain. Results from three sites will illustrate the capabilities of electromagnetic surveys.
The site of La Ciudad is a prehistoric Hohokam settlement located in what is now Phoenix, Arizona. A high conductivity zone in one area of the EM survey was tested by excavation. The anomaly was found to be caused by an unusual, dark clay-like layer extending to ca. 1 m underground. This is possibly a sedimentation basin; while it is within the area of the prehistoric settlement, it is not known whether it is natural or cultural, or even if it might be of the historical period. Test excavations in other areas, outside the small area revealed concentrations of ash, possibly remnants of debris mounds. These were not detected by the EM survey, for their electrical properties were too similar to the surrounding soil.