Figure 1. Hopeton Earthworks with the 2001 research area highlighted in gray, corresponding to the area shown in Figure 2.

Geophysical Survey

Geophysical survey work was conducted at the Hopeton Earthworks from May 12 through May 17, 2001. The geophysical survey work conducted by the Midwest Archeological Center was limited to magnetic surveys using a Geoscan FM-36 fluxgate gradiometer and a Geometrics G858 cesium gradiometer.
During the course of this research, the Midwest Archeological Center and Hopewell Culture National Historical Park sponsored a workshop on geophysical survey techniques. The contemporaneous scheduling of these two events allowed Dr. Bruce Bevan to conduct independent geophysical prospection studies at the Hopeton Earthworks site (Bevan 2001).

The 2001 geophysical survey at Hopeton Earthworks was conducted on the south side of the east-west farm road that passes through the square. The area surveyed is part of the overall Hopeton Earthworks grid system and is located between 2800 and 2900 north and between 2860 and 3160 east. Geophysical survey data was collected in blocks measuring 20 m x 20 m (Figure 1). A total of 47 blocks were surveyed, covering an area of 18,800 m².

Data was collected at intervals of 1.0 meter between transects. Forty-five blocks were surveyed with the G858 cesium gradiometer, and fourteen blocks were surveyed with the FM-36 fluxgate gradiometer.

The Geometrics G858 cesium gradiometer was in the vertical configuration, with the lower sensor 30 cm above the surface and the upper sensor 100 cm above the lower sensor. The survey was in the ‘walking’ mode using a 0.2-second cycle with traverses spaced at intervals of 1.0 meter, and readings spaced about 14 cm apart. The magnetic data map in Figure 2 provides a composite result of all the G858 survey blocks clipped at ± 10 nT/m. Since the sensor separation was 100 cm, the results are essentially total field data with the values numerically equal to nT.

The most notable accomplishment of the geophysical survey was the discovery that the western and southern walls of the square are very distinctly visible in the magnetic survey data (Figure 2). The sharp boundaries on the interiors and exteriors of the walls are in marked contrast to existing topography, which is very gradual due to years of agricultural activities.

The sharp magnetic contrast between the core of the wall and the surrounding soils suggested that the interior of the wall must have been constructed from a material that differed markedly from the soils that occur naturally on the terrace.

Magnetic survey data was used to select an area for test excavation that might best expose some of the better preserved sections of the wall. The strong magnetic lines marking the earthwork wall lines are separated by 10 to 15 m. The magnetic maxima are 15 to 20 nT. Breaks in the wall line anomalies correspond to the gateways mapped by Squier and Davis (1848) and Thomas (1894). We believe the east-west streaking that occurs at various places is the result of deep plow scars.

A subset of these blocks, plus two additional blocks, were surveyed with a Geoscan FM?36 fluxgate gradiometer. The FM-36 gradiometer is vertical, with sensors separated by 50 cm and the lower sensor at about 30 cm above the surface. The traverses were separated by 1.0 meter, and the readings were taken in the automatic mode with 8 readings per meter, which gives intervals of 12.5 cm. Examination of the data indicates that the G858 and FM-36 data sets are generally comparable.

An east-west line in Blocks AQ, AR, and AS was examined with several geophysical survey methods by Bruce Bevan (2001). He conducted a magnetic survey, and carried out a traverse with a GSM-19fg gradiometer. The sensor spacing was 1.5 meters and the lower sensor was 0.57 meters above the surface. The measurement interval was 0.1 meters.

A comparison of the data from this survey with the G858 and FM-36 indicates that all three surveys produced comparable results. The G858 maximum is about 11 nT/m above the background, and the maxima for the GSM-19fg and FM-36 are 8 nT/m and 6 nT/m above the background. The lower value for the GSM is because the lower sensor was higher above the surface. The lower value for the FM-36 is due to the smaller sensor separation in the instrument.

During the course of the magnetic survey of the wall, data was also collected from areas immediately inside and outside of the square wall. It was hoped that this survey data would identify anomalies that might represent features resulting from Hopewellian activities associated with the earthwork. Examination of the survey data resulted in the identification of 11 anomalies that might represent prehistoric features.

Topographic Survey

In June 2001, Archeologist Bruce A. Jones, Midwest Archeological Center, conducted a topographic survey of the research area. This was the first detailed topographic survey at the Hopeton Earthworks since Colonel Middleton surveyed the site for the Bureau of American Ethnology in 1890 (Thomas 1894).

The Midwest Archeological Center, with assistance of field school students from the University of Nebraska, Lincoln, and the Milton Hershey School, Pennsylvannia, conducted test excavations in the study area from June 13 through June 29, 2001. Test excavations consisted of four 2-x-2-meter units and a trench 48 meters north-south and approximately 1.5 meters east-west.

The four 2-x-2-meter test units were placed to expose four different anomalies. All four units were located adjacent to, or near, the exterior of the south wall of the square. Test units were assigned numbers corresponding to the arbitrary numbers assigned to the magnetic anomalies, so the four corresponding Test Units 2, 3, 4, and 6 were excavated.

Metal horseshoes were found in Test Units 2 and 3 that may have produced signals that were misinterpreted as prehistoric features. No evidence of a prehistoric feature was observed in Test Unit 3, but a horseshoe and modern agricultural disturbance may have produced Anomaly 3.

A large post hole was exposed at 1.0 meter below surface in Test Unit 2, so it is possible that the anomaly that was observed in this area was due to the post hole rather than the historic metal horseshoe fragment. Test Units 4 and 6 exposed two important prehistoric features that appear to be related to the Hopewell activities at the earthworks.

Trench 1 was about 1.5 meters wide and 48 meters long; it was located between 2880N and 2832N and between 3018.5E and 3020E on the site grid. The purpose of the trench was to transect a segment of the south wall of the square. The trench was excavated by backhoe.

The backhoe operator carefully removed small amounts of soil along the trench alignment, and archeologists were able to monitor the work and divert excavation when several possible features were exposed. After the backhoe removed the majority of the fill, the archeological team hand-excavated five possible features within the trench. Three of these proved to be prehistoric features.

Excavators cleaned the walls of the trench to expose them for further study by Dr. Rolfe Mandel, who spent two days at the Hopeton Earthworks with the research team. Dr. Mandel inspected the trench profile and noted that “the reddish fill strongly resembles a well-developed alluvial soil in the immediate vicinity of the site. Iron-bearing minerals in the parent material (sandy alluvium) were weathered during pedogenesis, thereby producing Fe2O3.”

The general construction sequence for this segment of the south wall can be reconstructed from the stratigraphy in the trench. First, all topsoil was removed from the area upon which the wall was built. This exposed a compact yellow clay-loam subsoil. Additional yellow clay-loam, similar to the subsoil base, was then brought in from another location and piled up to form a wall. A red sandy clay was then piled on the top and outside (south) of the yellow clay-loam wall. Then, topsoil was piled on the top and both sides of the wall. The contact between the yellow and red soils is very sharp, and it would appear that little time elapsed between these two construction phases (Figure 4).

The magnetic profile from the cesium gradiometer survey along the trench line (before excavation) had two strong, narrow maxima that must be related to the iron-oxide content of the soils. Micromorphological and magnetic susceptibility studies of soil columns are being conducted to further evaluate this interpretation. The trench profile revealed two ‘A’ horizons that sloped upward towards the middle of the wall segment and appeared to represent the original surfaces of the wall. These have been covered by slopewash from the top of the wall as a result of historic and recent agricultural activities.

The stratigraphy in this wall segment is only generally similar to that reported by Ruby (1997) for the north-west corner of the square. A second trench, planned for the west wall of the square, was not excavated in 2001 due to time limitations.

Features

Ten soil stains were initially assigned feature numbers during the excavation of the trench and test units. Seven of these appear to be the result of prehistoric cultural activities; the others are the result of rodent activity. Two post holes were recorded in Trench 1, and another was located in Test Unit 2. A fourth possible post hole or shallow pit was identified in the fill of the wall within Trench 1.

The other features included a burned log in Feature 6, which was located at the base of the wall in Trench 1, a fired-clay basin in Test Unit 4, and a large pit in Test Unit 6. These latter three features warrant further discussion and illustration.

Feature 1 is located in Test Unit 4 and represents a large clay basin that has been hardened by fire (Figure 5). The basin has a raised rim on the north and west sides and slopes slightly downward to the southeast. Although the feature extends into the east wall of the test unit, enough of the basin was exposed to note that it appears to represent a prepared clay surface that was hardened by repeated exposure to fIre. The basin contained burned soil, charcoal, and ash.

Several ceramic sherds were found on the northwest edge of the basin. Although this basin is not as symmetrical and well prepared as the features routinely called crematory basins at other Hopewell sites, it is clear that it is similar in form and construction. No bone was present in association with this feature, but the evidence for repeated fires is likely indicative of ritual activities.

Feature 6 is located at the eastern end of a segment of the south wall and appears to have been built at the edge of one of the many gateways to the square. The feature was located in Trench 1 near the base of the yellow clay that was piled up to form the first component of the wall. Two burned logs were lying horizontally at a level immediately above the undisturbed yellow clay subsoil upon which the wall was built (Figure 6). The feature appears to be contemporaneous with the start of construction on this segment of the wall and should provide sufficient carbon for radiocarbon dating.

Feature 9 is located in Test Unit 6, which is on the south side of the southern wall of the square. The feature is located about 10 meters outside one of the gateways in this part of the wall. The feature appears to be a large pit. The fill of the pit is similar in color to the surrounding subsoil, but the presence of abundant prehistoric artifacts, combined with a looser-textured soil in the pit, made it possible to distinguish the pit during careful excavation.

Only a sample of the pit fill was excavated, but fire-cracked rock, bladelets, pottery, and mica were abundant in the pit. Excavators recovered what appears to be part of a tetrapod ceramic vessel that contained mica. In numerous cases, small pieces of mica were found adhering to the interior surfaces of ceramic sherds.

A heavily used ground-stone celt was also found in the pit fill. Further analysis is necessary, but the pit may contain refuse from ritual activities or from the preparation of objects for ritual activities.

Summary

The 2001 research at the Hopeton Earthworks focused on the southern end of the square. Magnetic survey data provided evidence that the core of the wall was intact, and gateways dividing the wall into sections can be detected from the magnetic data. Several anomalies appear to indicate prehistoric features, and these were also recorded. Subsequent testing confirmed that the core of the southern wall of the square is still intact.

Field observation of stratigraphy detected a complex construction sequence that appears to have occurred over a relatively short time. Micromorphological and magnetic susceptibility analysis are planned to evaluate this interpretation. Strategic testing to examine four anomalies provided evidence for several features, including a fired-clay basin and a pit containing what appears to be refuse from ritual activities or preparation of materials for ritual activities. The methodology employed in 2001 appears to be effective in addressing the research problems and questions identified for this multi-year project.

References

Bevan, Bruce
2001 Geophysical Tests at the Hopeton Mound Group. Geosight, Weems, Virginia.

Dancey, William S. and Paul J. Pacheco (ed.)
1997 Ohio Hopewell Community Organization. Kent State University Press, Kent.

Lynott, Mark J.
2001 The Hopeton Earthworks: An Interim Report. Hopewell Archeology 4(2):1-5.

Mills, William C.
1922 Exploration of the Mound City Group. Ohio Archaeological and Historical Society 31.

Moorehead, Warren K.
1922 The Hopewell Mound Group of Ohio. Field Museum of Natural History, Anthropological Series 6:73-184.

Pacheco, Paul J. (ed.)
1996 A View From the Core, A Synthesis of Ohio Hopewell Archaeology. Ohio Archaeological Council, Inc.

Ruby, Brett
1997 Current Research at Hopewell Culture National Historical Park. Hopewell Archeology 2(2):1-6.

Squier, E.G., and E. H. Davis
1848 Ancient Monuments of the Mississippi Valley. Smithsonian Contributions to Knowledge No.1. Washington, D.C.

Thomas, Cyrus
1894 Report on the Mound Explorations of the Bureau of Ethnology. Twelfth Annual Report of the Bureau of American Ethnology for the Years 1890-91, Washington, D.C.

Acknowledgements: The authors thank Jarrod Burks for his assistance in the preparation of Figure 1, and John Andresen for his assistance in editing and formatting this paper.

About the Authors

Mark Lynott is Manager, Midwest Archeological Center. John Weymouth is Professor Emeritus, University of Nebraska, and winner of the 1998 Fryxell Award for his use of geophysical studies in archeology.