Ground Truth: Archaeological and Site Structure Implications for Recent Field Verification of Magnetic Surveys of Two Ohio Archaic and Woodland Sites
Kevin Schwarz, Jeffrey Weinberger
ASC Group, Inc.
Ohio Valley Archaeological Consultants, Ltd.
Recent archaeological assessments of prehistoric sites by ASC Group, Inc. and Ohio Valley Archaeological Consultants, Ltd. have led to an enhanced understanding of site structure and the relationship between plow zone artifact distributions and subsurface features at prehistoric sites in Ohio. The authors utilized magnetic survey to detect cultural features, followed up by focused ground-truthing excavations. The evolving use of this magnetic survey/ground-truthing methodology contributes to better understanding the structure of archaeological deposits and natural and cultural transformations (Schiffer 1995:37-38) within a given archaeological site. The identification and assessment of archaeological features within a cultural resource management context constituted the initial rationale for the development of this method. Surprisingly, the payoff has been that the methodology provided a window to understanding subsurface soil properties that can be exploited for archaeological and site structure information and for landscape archaeology (Kvamme 2003:435-436), leading to a more integrated and informative investigation. Our discussion is developed through case studies of two multi-component prehistoric sites investigated in Ohio.
The first site discussed is the Oberschlake #1 site (33CT648), a predominantly Late Archaic Maple Creek phase occupation located in Clermont County, Ohio (Schwarz et. al. 2005). The site consists of a large area of artifact concentrations that exhibit spatial patterning and is relatively undisturbed by plowing. Magnetic survey by Jarrod Burks located fifty seven magnetic anomalies at the site (Figure 1), so it was necessary to ground-truth the existence of prehistoric features through test pit excavations. ASC Group excavated test pits to verify or disprove the existence of cultural features. These excavations tested seven magnetic anomalies and five were found to be one or more prehistoric feature, including one fire pit which was radiocarbon dated to 4190ñ120 B.P. Beyond the goal of verifying the magnetic anomalies, the integrated methodology yielded other information of value.
Three peaks in artifact concentration are found within or adjacent to the anomaly cluster. Artifact clustering is noted for lithic debitage, which is most concentrated in a band that crosscuts the eastern edge of the anomaly cluster (Figure 1). Much lower densities of lithic debitage are present throughout the rest of the site, possibly resulting from repeated sweeping of activity areas (DeBoer and Lathrop 1979). The distribution of FCR supports the idea that artifact patterning at the site is related to refuse disposal patterns. Figure 2 shows that while FCR is present across most of the site, it occurs in dense concentrations in two places. One of these areas is near the center of the anomaly cluster, but not directly over any one anomaly. The second cluster of FCR occurs south and east of the anomaly cluster along the E1040 line, far from any magnetic anomaly. With no anomalies present in the vicinity of this FCR cluster, one interpretative possibility is that the inhabitants of the site were cleaning up some of their FCR since it could be considered to be a hazard (Burks 2004). Such cleaning is documented cross- culturally in medium to long-term habitations (Hayden and Cannon 1983; Kent 1990).
Site 33FR884, in Franklin County, Ohio, is a multicomponent site located on a small rise just north of the Hayden Run drainage, west of the Scioto River (Hartman Davis et al 2004, Weinberger et al 2005). The plow zone lithic assemblage recovered from the survey and assessment work contained Paleoindian, Late Archaic, and early Late Woodland diagnostic projectile points. Four relatively large lithic concentrations, consisted predominately of flakes and fragments of Delaware chert found in locally available in nodules and outcrops. A preliminary site function hypothesis identified the site as a repeatedly-used, secondary lithic reduction locus, similar to other sites in the immediate area. A geophysical survey, consisting of magnetometry and associated soil coring, identified potential cultural features. The combined fieldwork data, artifact analyses, and geophysical results suggested individual activity areas remained intact across the site, were temporally identifiable, and could aid in determining site structure.
Phase II investigations utilized a common grid for the geophysical survey and shovel testing. The magnetic survey noted 14 magnetic anomalies within the surveyed area (Figure 3) which were then compared against the shovel testing data. Test pit excavations documented two features that dated to the Early Woodland period (Feature 2) and early Late Woodland period (Feature 8). Feature 8 had ceramics determined to be Newtown or Peters Cordmarked ceramics (Prufer 1975; Seeman and Dancey 2000). In general, excavations at geophysical anomaly locations gathered both positive and negative data used to sort out likely activity areas. In this case, the data suggest that much of the production activity occurred in a specific location along the apex and slope of the landform, with Early Woodland activity likely centered near Feature 2 and Late Woodland activity centered around and north of Feature 8. In addition, the relative lack of lithic data or large anomalies from the center of the grid contributed to the site structure discussion. Essentially, the combined information collected during the Phase II work suggested multiple occupations conducting secondary lithic reduction of a nearby lithic source, with lithic, ceramic, and feature evidence suggesting a more intensive, sedentary Late Woodland occupation (Weinberger et al. 2005).
An integrated methodology shovel testing, magnetic survey and test pit
excavations can, in addition to locating cultural features, aid in understanding of site structure.
1) The investigation of 33CT648 yielded considerable information of a complex site structure probably due to differential use of space and disposal patterns.
2) The investigation of site 33FR884 determined it to be a locus of overlapping areas of lithic reduction. The magnetic survey aided in understanding the relationship between the features at the site and these activity areas and to infer locations of temporal components associated with a site repeatedly used for lithic reduction.
In each case, the integration of geophysical survey, enhanced and guided the development of the investigation and contributed more information toward the resolution of the research hypotheses, than a similar strictly excavation-based methodology would have allowed.
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