Geophysical Investigations at a Civil War Field Hospital

The Harper House, located in Four Oaks, NC is part of the Bentonville Civil War Battlefield State Historic Site.  The Battle of Bentonville was a gruesome Civil War clash that covered tremendous acreage.  This study is centered at the Harper House, the private home turned field hospital.  The main research objective was to study and identify the unseen structures and features that tell the story of the historic cultural and physical landscape.   Another goal was to locate potential sites of buried outbuildings and other structures and pits associated with the Harper House hospital activities.  An extensive geophysical survey of the subsurface was completed in March 2014.  The geophysical sensors used included Ground Penetrating Radar (GPR) and a Magnetic Gradiometer.  The survey results indicated areas of interest for further exploration.  Subsequently, an archaeological excavation was performed in June 2014 aiding in the validation of the survey results.  The excavation assisted greatly in the identification of both the physical and cultural subsurface features.   Using the data and analysis from these sensors, two trenches and three test units were established in June for the public archaeology event.  The objective was not only to determine what was being seen in the subsurface data, but to validate the accuracy of the sensors themselves.  The two trenches were placed due to the depth in which the high amplitude returns indicated a buried surface.  While one trench provided evidence of a trash pit with contents of historic value the other trench did not produce any archaeological evidence.  The GPR indicated an undulating surface in the second trench. However, excavation deemed it not to be archaeological in nature, but geologic.  A clay layer shows up as highly reflective in the GPR data appearing as a buried surface.  Though the archeological material was not found in the second trench, the results provided an important finding for geophysical investigations in both understanding the physical landscape of the property and validation of the GPR and Magnetometer collects.  As previously stated, three other smaller test units were also placed.  The most significant unit included a pipe that truncates into the yard that is also visible in historic photos seen extending from the old wing of the house to the yard.  This was a valuable finding for the validation of geophysical data.  The GPR and magnetometer precisely located the end point of the pipe.  The experience of this exploration into the physical and cultural landscape of the Harper House was tremendous.  Demonstrating how geophysical surveying techniques in concert with traditional archaeological methods could prove successful.  The poster that would be submitted associated with this abstract would emphasize the geophysical tools and techniques for mapping and modelling the subsurface.  Results from the excavation would be shown only as examples of validation of the geophysical sensors.