Geophysical Detection and Assessment of Leveled Mounds: An Example from the Upper Mississippi Valley

Abstract

Most earthen burial mounds of eastern North America have been destroyed—or have they? We review geophysical methods for assessing whether leveled mounds retain intact deposits or features. Magnetic survey holds promise for locating and evaluating leveled mounds because it is rapid and sensitive to magnetic variations associated with anticipated features such as pits and deposits of mound fill. As a case study, we discuss our magnetic survey of the Gast Farm site (13LA12) in eastern Iowa. The survey covered 8.64 ha, encompassing loci of one previously reported mound and possible geometric earthworks as well as Middle and Late Woodland habitation areas. Interpretation of survey results incorporated quantitative differentiation of magnetic anomaly types using GIS techniques, along with standard visual inspection. We found no evidence of geometric earthworks but identified at least six leveled mounds. Displaced mound fill appears to account for the earthwork-like features. We conclude that leveled mounds are detectable and may retain subsurface integrity. Their associated features, including burials, may be identifiable even when above-ground evidence has disappeared.