North American Database of Archaeological Geophysics
North American Database of Archaeological Geophysics
Abstract/Summary:
Project Name: Effigy Mounds, IA (2);
Reference: Dalan, R.A. (2000). Suceptibility Sampling of Mound 19, Effigy Mounds National Monument, Iowa. Department of Anthropology and Earth Science, Minnesota State University Moorhead, Moorhead, Minnesota. Prepared for the National Park Service, Midwest Archeological Center, Lincoln, Nebraska.
This report presents the results of magnetic susceptibility sampling conducted in conjunction with the National Park Service's workshop "Recent Advances in Archaeological Prospection Techniques" held May 10-14, 1999. This workshop was co-sponsored by the Midwest Archeological Center, the Iowa Office of the State Archaeologist, and the Effigy Mounds National Monument.
This project was designed to characterize vertical and horizontal patterns in susceptibility across mound and off-mound areas as a preliminary step in assessing the utility of susceptibility studies at the site. Susceptibility samples were collected from Mound 19, which is part of a linear mound group in the North Unit of Effigy Mounds National Monument. Samples were also collected from surrounding off mound areas.
Susceptibility data collected from Mound 19 and the surrounding area indicate that local materials were used for the construction of this mound. Indeed, the data show that it is near surface topsoil that was used as mound fill. The susceptibility data thus agree with the research of Parsons (1962) who came to this same conclusion about patterns of mound construction at the Effigy Mounds National Monument some 30 years earlier. Parsons further showed that the topsoil had been gathered from the area beneath the mounds with this being augmented by topsoil from areas surrounding the mound. The susceptibility data produced as part of this project are not sufficient to support or reject this model for Mound 19.
The susceptibility data also agreed with a conclusion reached by Bevan (1999) about subsurface layering in the vicinity of Mound 20, located directly to the east of Mound 19. Bevan concluded that the same general subsurface layering was present across the mound as in off mound areas; the only difference was a thicker surface layer at the mound location. An increased complexity or "lumpiness" of mound fill compared to surrounding soils, as concluded from seismic surface wave studies at Mound 20, was not noted in the susceptibility analysis of materials from Mound 19.
Several anomalous areas were revealed by the susceptibility research. Two of these (the Core K and Core L) locations, were targeted for coring based on anomalies noted during preliminary resistance and magnetometer surveys. Susceptibility profiles at these locations, as well as for the core located in the open field (Core M), showed relatively thin and weak enhanced susceptibility layers. Erosion of surface soils at these locations is one possible explanation.