Archaeo-Physics, LLC - geophysical survey and subsurface mapping

Case Study

Songbird Rings

Big Horn County, Montana

Songbird Rings (24BH1162) is a prehistoric archaeological site in southeastern Montana. The "rings" referred to in the name of the site are stone rings (also called stone circles or tipi rings), a type of archaeological feature characteristic of prehistoric campsites on the Great Plains. Composed of natural stones arranged in a circular pattern, they are usually interpreted as having weighted down the edges of tipis or other types of circular tents (although there are exceptions where this seems unlikely).

Where the rock that comprises the stone ring is of igneous origin, it may be detectable by magnetometer survey, allowing these features to be mapped even where they are not exposed. Even when partially exposed, circular patterning may not be readily apparent, and magnetic mapping can be valuable in distinguishing cultural from natural distributions of stones. Sedimentary rocks are generally more difficult to detect by magnetic methods, although in the case of Songbird Rings, the stone rings were composed of scoria - sedimentary rock thermally altered by burning coal seams, rendering it highly magnetic.

A magnetic gradiometer was used to survey several areas within the Songbird Rings site. The results from one of these survey areas are shown below. At this time, preliminary testing has largely confirmed magnetic survey interpretations, but the site has not been excavated or extensively tested.

Mouse over image to display interpretations

Magnetometer survey results showing stone (tipi) rings and prehistoric hearth features
  • Two stone rings are readily apparent as roughly circular patterns of bipolar anomalies. The positive and negative components of these anomalies represent the poles of the magnetic fields of individual rocks within the ring.
  • Four anomalies are present (circled in yellow) that have been confirmed by subsurface testing as prehistoric hearths. Hearth features are often detectable magnetically, typically appearing as moderately strong circular magnetic highs (although other expressions are also seen).
  • Several anomalies circled in black are suspected as prehistoric features, but have either not been tested, or initial testing results have been inconclusive.

Geophysical survey of the Songbird Rings site was performed by Archaeo-Physics as part of an archaeological investigation under the direction of Gene Munson of GCM Services, Inc. The project was commissioned by Westmoreland Resources, Inc. as part of an assessment of cultural resources in areas of potential impact by mining.

Related content:

Papers and publications - Geophysical Survey as an Approach to the Ephemeral Campsite Problem: Case Studies from the Northern Plains

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