A Geoarchaeological Overview of South Dakota and Preliminary

DRAFT DRAFT DRAFT
components. The basic rational for trench numbers and placement should be outlined by the survey team
as part of the work plan supplied to Mn/DOT” (Monaghan et al. (2005).
Excavation to as deep as the backhoe will reach, ca. 3-4 m, is recommended unless the water table or
basal deposits are encountered. The protocol stipulates methods for profiling, flotation sampling, and
radiocarbon dating.
Like trenching, coring or augering first establishes the depth to basal deposits.
The principal goal of the coring process is to identify stratigraphic horizons that represent stable
surfaces of an age compatible with human occupation. These are identified based on their
stratigraphical, pedological, and sedimentological characteristics. The depths to the top and base of these
horizons are defined based on the core data, and then these target horizons are sampled with augers for
the buried archaeological materials.
To sample the “target horizons” using augers, the protocol pilot project used mechanically-drilled
flight augers, 10-13 cm in diameter and (typically) 1.2-1.8 m long. An example of a flight auger is the
screw-type drill attached to the power augers commonly used for subsurface testing in the Dakotas.
Those used on core and drill rigs are designed to connect together into long, continuous strings, called
“flights.” The pilot study did augering on 20 m grids. At each point on the grid, multiple auger holes
were drilled, enough to test a sampling volume equivalent to that of a 25 cm diameter shovel test. This
required 4-6 individual holes, depending on auger diameter.
Discussion
The guidelines presented above view deep testing as part of Level-III-equivalent intensive survey. A
difference between them is that Iowa’s recommends that geomorphological study be conducted in
advance of the archaeological survey (Association of Iowa Archaeologists 1993). The rationale is that
archaeological survey of alluvial, colluvial, and eolian landscapes should not begin until the
archaeologists know about subsurface conditions. For example, pedestrian surface survey need not be
undertaken in areas covered or entirely underlain by historic-period alluvium, where surface prehistoric
sites will not exist. Further, the premise is that, prior to starting subsurface testing, archaeologists should
know where and how deep testing should extend.
In practice, in Iowa, the additional time and cost of “doing the geomorphology first” has proven to be
impractical except for relatively large projects where complex depositional sequences make an initial
geomorphological investigation essential. For small and quite a few large projects, archaeologists
working in Iowa generally do the geomorphology “as they go.”
The Minnesota protocol summarizes the relationship between geomorphological and archaeological
investigations as follows,
“The discovery and evaluation of buried archaeological sites is a multidisciplinary task that focuses
on two different aspects of geoarchaeology. The first, discovery, emphasizes the “geology” of
geoarchaeology while the second, evaluation, focuses on the “archaeology” of the discipline.”
To that extent, the Indiana guidelines and Minnesota protocol, as well as other states, establish a
methodological approach that accomplishes both the geology and the archaeology at the same time. For
example, both documents recommend that trenching proceed in systematic intervals, carefully peeled
back with a smooth-bladed bucket to find artifacts as well as expose stratigraphy. Flight-augering in the
Minnesota protocol is designed to sample volumes equivalent to a standard shovel test.
Not surprisingly, in the field, the Iowa “do it first” and Minnesota/Indiana “do it together” approaches
are rarely mutually exclusive. The Minnesota protocol requires that subsurface testing begin with a
geologically oriented effort to find the depth to basal deposits, followed by closer interval trenching or
augering to search for sites. In Iowa, archaeologists will frequently skip over, or widen sampling
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