North American Database of Archaeological Geophysics

Abstract/Summary:

Project Name: Double Ditch Indian Village State Park (32BL8), ND;

References: Kvamme, K.L. (2000). Geophysical Explorations at Double Ditch Indian Village State Park (32BL8), Burleigh County, North Dakota. Department of Anthropology and Center for Advanced Spatial Technologies, University of Arkansas, Fayetteville, Arkansas. Submitted to the State Historical Society of North Dakota.

Kvamme, K.L., and J.A.C. Kvamme (2001). New Insights About The Structure Of The Double Ditch Site, North Dakota, Through Geophysical Surveys. Paper presented at the Plains Anthropological Conference, Lincoln.

Kvamme, K.L. (2002). Report of Geophysical Findings at the Double Ditch State Historic Site (32BL8): 2001 Investigations. Submitted to PaleoCultural Research Group, Flagstaff, Arizona, on file at the State Historical Society of North Dakota, Bismarck.

Kvamme, K.L., and J.A.C. Kvamme (2002). Double-Double Ditch? New Insights Concerning Double Ditch (32BL8) Gained Through Geophysical Surveys. Paper presented at the Plains Anthropological Conference, Oklahoma City.

The Double Ditch site (32BL8), located on a high terrace above the Missouri
River immediately north of present day Bismarck, is preserved within a state
park, the Double Ditch State Historic Site. When Lewis and Clark passed by
in 1804 it had probably been abandoned by the Mandan for a couple of
decades, most likely due to a smallpox outbreak in the 1780s. It has always
been understood that Double Ditch is an unusually large site. At
approximately 4.8 ha within the second or outer ditch seen in the
topography, it is one of the largest fortified settlements along the Middle
Missouri River. It is also distinctive in the size and number of its large
midden mounds, some over 3 m, the many shallow depressions 12-18 m in
diameter that signify the loci of former houses, and its readily apparent
double fortification system from which it derives it's name.

A small exploratory geophysical survey was undertaken at this site in 1997
that indicated good subsurface contrasts and anomaly definition in
magnetometry and resistivity data. Approximately 1.7 ha of magnetic and
resistivity survey was accomplished in 2001 that sampled the known site area
in a series of transects. Magnetometry, in particular, yielded a number of
new insights. (1) Numerous 1-1.5 m diameter circular anomalies, distributed
largely outside of houses, were mapped that mostly represent storage pits.
(2) A number of rectangular-shaped houses were better defined (beyond their
visible surface depressions) with such interior features as central and
auxiliary hearths and storage pits revealed in the data. (3) Two very large
circular borrow pit areas were made clear, measuring 32 and 50 m in
diameter, that are devoid of anomalies. They are interpreted as places where
soil was mined, possibly for earthlodge construction. (4) A number of linear
features were revealed in the data that coring suggested were shallow ditch
features, but their function could not be explained.

The resistivity data gathered in 2001 were less insightful, but nevertheless
produced several important results. The resistivity data tend to indicate
midden mounds as high resistivity features, probably owing to their
generally increased dryness that is due, in part, to a topographic effect
(high points tend to be drier), but also to decreased compaction and their
being a focus of intensive rodent activity (larger pore spaces). The data
also point to some high resistivity features, quite possibly dispersed
middens that are not visible as mounds on the surface. Another phenomenon
that the resistivity data tend to emphasize is a zone of high resistivity
around the perimeter of many of the obvious house depressions. They are
interpreted as zones of “roof melt,” eroded sediments from earthlodge roofs
that may exhibit high resistance owing to compaction differences and the
topographic effect.

The geophysical work in 2002 will change forever the way we view Double
Ditch and, indeed, certain aspects of northern Great Plains prehistory. An
additional 2.1 ha of magnetic survey, 1.9 ha of resistivity, and a more
limited amount of additional GPR work was undertaken. The most significant
finding is not one, but two additional fortification systems that surround
the village. Of equal importance are the presences of systematically placed
bastions whose forms point to a much greater antiquity of the site than
previously thought. Several additional discoveries and points are
emphasized.

(1) The lineations seen in the 2001 data form parts of the fortification
rings, but they were not recognized for what they were at the time.

(2) The new fortification ditches are not visible on the surface, unlike the
two well-known ditches that give the site its name.

(3) Anomalies that occur within the areas enclosed by the new fortification
systems do not appear to represent houses, but only storage pits. The
absence of houses in these outer zones is puzzling.

4) The area of Double Ditch, as measured within the outer fortification
system, is significantly greater than previously thought, making it one of
the largest fortified settlements in the region. An estimate of the area
within the outer defensive work, based on the currently incomplete mapping,
is about 7.5 ha.

(65) The Double Ditch State Historic Site needs a new name (e.g., “Quadruple
Ditch,” “Double-Double Ditch”)!

Besides evidence of rectangular houses, there is good evidence of circular
earthlodges in the magnetic data as well. These findings support the
inference of a long occupation from perhaps the 15th century to immediately
before the time of Lewis and Clark.

The resistivity survey, now totaling 3.6 ha, was performed with a target
depth of 50 cm to better image the many features that we now know are closer
to that depth. Possibly owing to the unusually hot and dry summer or to
inherent soil properties, resistivity contrasts were somewhat poor or even
non-existent in the vicinity of the newly discovered fortification systems,
but provide important evidence that corroborates the magnetic findings. A
puzzling result is that certain portions of these ditches exhibit a more
common low resistivity, while other segments indicate high resistivity. This
phenomenon cannot be explained at this time, but perhaps indicates
differences in the nature of the fills.

At Double Ditch, thanks to geophysical surveys, we now know we have a truly
gigantic settlement of much greater complexity, time depth, and
significance. We hope that additional geophysical work will be possible in
the future to completely map this settlement and it's defenses, and to
discover yet more fortifications about this world class site.

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