Assessment of various geophysical techniques for Plains Indian archaeological site investigations

Abstract

Development of the Missouri River Basin was authorized by the Flood Control Act of 1944 when six main stem dams were sited along the Missouri River. Construction of these darns has created a series of lakes which are currently experiencing high rates of shoreline erosion. Under the auspices of the Antiquities Act of 1906, the National Historic Preservation Act and the Archaeological Resources Protection Act, erosion of the lakeshore bluffs is of concern because of the presence of Native American archaeological sites on the terraces. Erosion of the bluffs has proven that culturally important sites which have no recognizable surface expression are in imminent danger of being lost. The problem addressed by this study was the assessment of various geophysical techniques for non-intrusive location of Plains Indian archaeological features. Plains Indian cultural resources are being lost because of the rapidly eroding shorelines and the lack of a quick and cost-effective method for locating the sites. A need exists for a quick and effective method for the delineation of sites which would otherwise remain unknown. To meet this need, non-intrusive geophysical techniques offer the greatest potential. Several known archaeological sites were selected along the banks of Lake Sharpe, South Dakota for surveying. These sites were surveyed using geophysical techniques identified as having the most potential to rapidly locate anomalies characteristic of buried archaeological features, ground penetrating radar, magnetics, and earth conductivity. The results of the ground penetrating radar surveys show that the surface conditions at the sites can prevent collection of interpretable radar data. Heavy vegetation at the sites produced data records which proved difficult to interpret. The results of the conventional magnetics technique showed no magnetically anomalous artifacts or conditions at the sites. The results of the earth conductivity technique yielded anomalous readings over several of the known features which showed surface expression in the form of depressions. A high volume of rainfall and low temperatures during the study period are believed to have created homogeneous subsurface moisture conditions which made soil moisture anomalies associated with features showing no surface expression difficult to locate.