Archaeo-Physics, LLC - geophysical survey and subsurface mapping

Case Study

The Huckins Site (48WE917)

A Prehistoric Campsite in Weston County, Wyoming

 

magnetic gradiometer survey - detail
Magnetic Survey

 

  resistance / resistivity survey  - detail
Resistance Survey

Archaeo-Physics LLC was contracted by GCM Services, Inc. to perform a geophysical investigation as part of archaeological investigations at 48WE917, a Late Archaic site in Weston County, Wyoming. The geophysical investigation consisted of magnetic field gradient surveys of several areas within the site, and an electrical resistance survey of a small area within one of the larger magnetic survey areas.

Based on artifacts recovered from the surface, the Huckins site appears to have been repeatedly occupied from at least the Late Archaic to Late Prehistoric periods. Open air campsites such as Huckins are often a composite of clusters of features and artifacts. This type of site may cover hundreds if not thousands of square meters, but in reality there are large areas within it that are virtually devoid of cultural remains. The geophysical survey was undertaken as part of phase II evaluation of the site in order to identify loci that might be associated with different occupations and activities. It is unlikely that conventional methods alone could produce a large enough sample of positive data for meaningful description and hypothesis testing on a site of this size and complexity.

Lithic tools and debitage and fire cracked rock were scattered across the site, and several hearths were visible on the surface. Very few modern artifacts were found.It was anticipated that in an archaic cultural context, hearths were likely to be the most detectable cultural features. Magnetic field gradient survey was chosen as the principal method of investigation because the thermally altered mineral grains in rock and soil often create a strong and distinctive magnetic anomaly.

The magnetic field gradient and electrical resistance surveys were successful in detecting probable cultural features all of the areas surveyed. Anomalies of interest appear in discrete clusters, generally near the edge of the flat top of the landform. These clusters may represent separate social units or successive occupations.
Most of the suspected features are thought to be hearths. Correlation between exposed hearths and magnetic anomalies allows a high degree of confidence in the interpretation of these anomalies. A number of other anomalies appear to be culturally patterned, but cannot be as easily interpreted without ground truthing. Results of the resistance survey were more ambiguous, but there is some correlation between resistance and magnetic data sets.

In general, the site had very little magnetic "clutter" due to modern metal or geologic variance. The standard deviation of each of the survey areas ranged from 0.16nT to 0.64nT (after processing). Anomalies thought to be caused by hearths have amplitudes up to several tens of nanoTeslas and contrast starkly with the very uniform background. Anomalies thought to be caused by hearths appear as discrete magnetic highs with values ranging roughly from 1nT to 50nT. While in-situ hearths often appear as bipolar anomalies because of remanent magnetic effects, hearths at 48WE917 appear with only a very weak negative component. An explanation for this is that bioturbation and other small-scale disturbances may have randomly re-oriented mineral grains in the soil. Remanent effects are thus largely neutralized, leaving only an induced-field anomaly caused by enhanced suscuptibity. Other more subtle magnetic highs appear that may be caused by other types of features, such as houses and pits.

Related content: Geophysical survey as an approach to the ephemeral campsite problem

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