North American Database of Archaeological Geophysics
North American Database of Archaeological Geophysics
Abstract/Summary:
Project Name: Ponca Cemetery, NE;
Reference: Weymouth, J. W. (2000). A Magnetic Survey at the Cemetery of the Ponca Tribe of Nebraska. University of Nebraska, Lincoln, Nebraska. Submitted to the Ponca Tribe of Nebraska, Niobrara, Nebraska.
This report summarizes the results of a magnetic survey conducted at the cemetery of the Ponca Tribe of Nebraska prior to the construction of a gate structure at the entrance to the cemetery. The survey was done to see if it was possible to detect graves using geophysical methods commonly employed in archaeological investigations in order to avoid impinging on any unmarked graves in the gate area.
The Ponca Tribe cemetery is located five miles northwest of the town of Niobrara, Nebraska. It is roughly 200 meters square in area, lies in rolling hills and is surrounded by a barbed wire fence. To the east and north of the cemetery is a field containing a buffalo heard owned by the Ponca Tribe. We divided the area of interest into squares or blocks 20 meters on edge. Blocks A and B covered the gate construction area. Blocks C and D covered areas of marked graves. We chose these latter areas in order to have survey signals or anomalies characteristic of graves to use as controls against which to compare possible signals of unmarked graves.
The instrument used was a Geometric G858 Cesium Gradiometer. In this instrument two cesium vapor censors are placed one above the other with the upper reading subtracted from the lower reading. The lower sensor was 0.3 m above the surface. The upper sensor was 1.2 m above the lower sensor. Because of the large sensor separation the difference readings approximate a total field reading. This operation cancels out time changes of the magnetic field as well as suppressing long-range trends in the background field.
The magnetic data revealed that there are many more anomalies in Block C, which is known to have graves, than in Blocks A and B. Because of shortness of time we used a grid interval of 1 m in Block D instead of ½ m that was used in all the other blocks. There is a distinct difference in the anomalies in Block D; the anomalies are much stronger and broader than in the other three blocks. The breadth is partially a result of using a large grid interval, but that does not explain marked difference in the strength of the anomalies. The difference is a result of some feature of the graves in this area. I suspect that these graves, as distinct from the graves in Block C, were internments that used vaults. I believe that only one grave in Block C, the one in the Northwest corner, used a vault. The marked difference in the anomalies in Block D prevent us from using this block in comparing the anomalies with those in Block A and B. . I have examined all the profiles of the marked anomalies and have concluded that a few of them could possibly have sources that are unmarked graves, although I have strong doubts.