North American Database of Archaeological Geophysics

Abstract/Summary:

Project Name: Effigy Mounds, IA (4);

Reference: Kvamme, K.L. (1999). Archeo-Geophysical Surveys at Effigy Mounds National Monument, Iowa. Department of Anthropology and Center for Advanced Spatial Technologies, University of Arkansas, Fayetteville, Arkansas. Submitted to the Midwest Archeological Center, U.S. National Park Service, Lincoln, Nebraska.

This report summarizes several geophysical surveys conducted in Effigy Mounds National Monument, Iowa. These surveys were performed with the assistance of students enrolled in the National Park Service sponsored workshop: "Recent Advances in Archaeological Prospection Techniques," held at the monument from May 10-14, 1999. During the course of the workshop three effigy mounds were geophysically examined by magnetic and resistance survey methods: Mound 52 (Little Bear), Mound 31 (Great Bear), and Mound 82 (a bird effigy). Two small circular mounds were also surveyed in the vicinity of the Great Bear. All of these mounds exist within forest clearings and are covered with relatively short grass.

The following generalizations and inferences can be offered from the geophysical results.

1. The effigy mounds are composed of more magnetic and more resistant materials. The elevated magnetic measurements may indicate the mounding of A horizon soils to build the effigies. The greater resistance values that were measured in the effigies may be partially due to reduced ground moisture as water drains out of the effigies after rain showers.
2. The "shadow" of negative values around the effigy perimeters may reflect the removal of generally more magnetic A horizon soils for the construction of the effigies.
3. The low resistance measurements seen around effigy perimeters are probably due, in part, to increased ground moisture, particularly around Mound 52 (Little Bear) where the gravel outline may act as a mulch.
4. The data show considerable "clumpiness" of magnetic and resistant earths that may point to building episodes, such as the construction of individual parts of the effigies and even the dumping of individual or multiple basket loads of earth. Some of the concentrated magnetic highs within the effigies may point to fired areas within the mounds.
5. The resistance data suggest that the head and foreleg of the Little Bear (Mound 52), and the tail of the bird effigy (Mound 82), may be separate constructions because of their lack of continuity with the remainder of the mounds.
6. Resistance holes seen in the effigies at about 0.5 m depth may indicate former pot holes or tree removals.
7. In all the effigy mounds examined, the head areas are very distinct and differently shaped magnetically, suggesting construction and shaping with a more magnetic earth, and perhaps firing within.
8. Ears are well defined magnetically in both bear effigies, compared to the electrical resistance responses and the shapes of the mounds themselves.
9. The data from Mound 31 (Great Bear) reveals a narrow and concentrated magnetic core, much thinner than the mound itself, suggesting an important construction (or perhaps NPS reconstruction) detail for this effigy. It is recommended that these results be considered in conjunction with the many other data sets acquired during the remote sensing workshop, and previous to it by other researchers.

Back to database entry