Geophysical Survey as an Approach to the Ephemeral Campsite Problem: Case Studies from the Northern Plains
Jones, Geoffrey, Munson, Gene, Plains Anthropologist
Temporary campsites and indeterminate artifact scatters are a perennial problem in archaeology. Features and artifacts are few, often scattered across an extensive area and representing considerable time depth. Meaningful and cost-effective data recovery is difficult using conventional methods. Integrated with more traditional methods, geophysical methods have proven to be an effective approach on many sites on the northwestern Great Plains. Hearths, stone rings, and other features can be detected and mapped, allowing researchers to target areas for excavation and understand intra-site patterning.
Keywords: magnetic survey, gradiometer, campsite, geophysics, hearths
Temporary campsites and indeterminate artifact scatters form a large percentage of prehistoric sites throughout North America, and especially on the northwestern Great Plains, where village sites are rare. It is obvious that our understanding of prehistoric lifeways is incomplete, if not deeply flawed, without understanding temporary campsites. Unfortunately, cost-effective data recovery from these sites is problematic using conventional sampling and excavation methods. Diagnostic artifacts and datable features are often present (or may be presumed to be present) but they are few and often scattered across an extensive area. When only a small percentage of a site may be sampled, recovered data are often inadequate to address meaningful research questions. Often these sites have distinct intra-site patterning and multiple components may represent considerable time depth.
Hearths and stone rings (tipi rings) are the most typical features of campsites on the northern Plains (for the purposes of this article, the term hearth is broadly used to indicate a variety of thermal features). Magnetic field gradient survey has been proven to be highly successful at detecting thermal features, and in certain conditions, stone rings, as well. Although this article focuses on a single method, there are a number of other geophysical methods commonly applied to archaeology. These case studies are generally illustrative of a geophysical approach, discussed in broader terms in a concluding section. As part of an integrated research strategy, geophysical mapping can allow researchers to better target areas for excavation, to collect a larger sample of positive data within limited budgets or schedules, and to study intra-site patterning beyond the limits of excavation.
The case studies presented in this article were selected from the results of 55 discrete survey areas at 21 prehistoric campsites in Campbell and Weston counties in northeastern Wyoming, and in Rosebud and Big Horn counties in southeastern Montana (Figure 1). They have been selected because they are illustrative of issues associated with this approach. Most of the 55 survey areas contained anomalies thought to be caused by prehistoric hearths or other archaeological features, and they are reasonably well represented by the specific case studies presented here. Geophysical data collection was performed between 2000 and 2003 by David Maki and Geoffrey Jones of Archaeo-Physics, LLC, as part of the archaeological treatment of these sites under the direction of Gene Munson of GCM Services, Inc. (Munson 2002a, 2002b, 2003a, 2003b, Munson et al., 2004).
While an in depth discussion of magnetic theory, survey logistics, and data processing is beyond the scope of this article, both Clark (1996) and GafFney and Gater (2003) provide excellent introductions to archaeological geophysics. Survey logistics, data processing, and technical parameters are dealt with in individual reports of investigation (Jones 2001a, 2001b, 2003). A brief non-technical introduction to magnetic field gradient survey is presented in the following paragraphs.
The geophysical surveys presented in this article were performed with a Geoscan FM36 magnetic gradiometer (Figure 2). This instrument records local variations in the earth's magnetic field, primarily caused by differences in the magnetic properties of subsurface materials. …