North American Database of Archaeological Geophysics

Abstract/Summary:

Project Name: 48WE917, WY;

Reference: http://www.archaeophysics.com/48WE917/index.html (used with permission).

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. 48WE917 is located on the top of an isolated dissected upland. Soils are sandy, with depth to sandstone bedrock (presumably the parent material) varying from zero to more than two meters. Ground cover within the survey areas consisted mainly of short grasses, sagebrush and other herbaceous plants, with scattered yucca. Scattered ponderosa pines, mainly on slopes at the edges of survey areas, were occasional obstacles to survey.

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 in 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 susceptibility. Other more subtle magnetic highs appear that may be caused by other types of features, such as houses and pits.

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