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
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
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
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
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).
on image to enlarge
|Comparison of the magnetic map (Figure
2) and the topographic map (Figure
3) of the study area indicates that the
magnetic maxima lie within the area of
highest topography, but that the magnetic
maxima are closer together while the
topographic data shows that sediments
from the wall are more widely spread.
2. Magnetic map of the Hopeton Earthworks,
south part of the “square.”
on image to enlarge
|Visual examination of the site and
the topographic map clearly shows that
the wall has been flattened by cultivation.
However, it is interesting that the material
causing the magnetic high in the wall
has not been dispersed by the spreading
out of wall soils by plowing.
3. Topographic map of the Hopeton Earthworks,
south part of the “square.” The
contour interval is 0.5 m.
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
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
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
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.
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.
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
2001 Geophysical Tests at the Hopeton Mound Group. Geosight, Weems,
Dancey, William S. and Paul J. Pacheco (ed.)
1997 Ohio Hopewell Community Organization. Kent State University Press,
Lynott, Mark J.
2001 The Hopeton Earthworks: An Interim Report. Hopewell Archeology
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.
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.
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,
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
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.