In December of 2008 a geophysical investigation was conducted at two archaeological sites located in the oil and gas fields of west-central Wyoming. The investigations were conducted for Current Archaeological Research, Inc in advance of Phase III mitigation of the sites, which is scheduled to begin in early 2009. Both of the sites were discovered by Current Archaeological Research staff archaeologists during the monitoring of cut and fill operations associated with new well pad construction.
The results of the geophysical investigation will be used to target features for excavation during Phase III mitigation (site excavation) prior to construction of new well pads. The survey results and interpretations can be viewed using the interactive data exploration tools presented below. Viewers must have a current FLASH PLAYER installed on their browser.
This case study illustrates many of the challenges inherent to applying geophysical methods to real-world cultural resource management (CRM) projects in North America. For example, these sites may be described as ephemoral - often identified by an light scatter of lithic artifacts and the presence of small shallow basin shaped features less than one meter in diameter, sometimes within house features defined by alignments of small diameter post molds (<10 cm). Additional challenges encountered during this project included: frozen soils; soil disturbance associated with earth moving by heavy equipment; and significant bioturbation.
Detecting such small and ephemeral targets under less than ideal conditions requires very high data sample densities, rigorous data quality control, and very thorough post survey analysis and interpretation.
In spite of the challenges discussed above, the geophysical survey did identify suspected archaelogical features at both sites, as well as create detailed maps of what appear to be prairie dog burrows and tunnels. The sites are scheduled for excavation during the 2009 field season. Excavation results will be posted on this page as they become available.
48SU4396
An interactive data exploration tool examining ground penetrating radar (GPR) and magnetic field gradient survey data from a 30 x 30 m grid at 48SU4396 is presented below. The exploration tool was designed to allow the user to explore the GPR imagery in detail, as well as overlay the magnetic survey results and compare the two data sets. Interpretations can be viewed by clicking the appropriate menu item. At 48SU4396 two regions of archaeological soil staining were discovered during mechanical scraping of the site. These regions (referred to as Tarped Areas A & B) can be viewed by clicking the upper left button under the Interpretations Menu.
Four sources of geophysical signal are suspected at 48SU4396. These are:
1. Disturbance associated with soil removal by heavy equipment (soil scraping).
2. Signal caused by changes in soils and/or geology.
2. Bioturbation, probably including a complex network of prairie dog burrows and tunnels.
3. Archaeological features.
Examples of all four suspected sources of geophysical signal can be viewed by clicking the appropriate menu items under the Interpretations Menu. Suspected archaeological features are labeled 1 through 4 in the Interpretations Menu. Additional archaeological interpretations may be viewed by overlaying the magnetic data imagery.
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48SU2229
An interactive data exploration tool examining ground penetrating radar (GPR) and electrical resistance survey data from a 20 x 20 m grid at 48SU2229 is presented below. The suspected sources of signal response are similar to those listed above for 48SU4396. Suspected archaeological features are labeled 1 through 3 in the Interpretations Menu. Additional archaeological patterning may be viewed by overlaying the electrical resistance imagery.
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Data Collection
GPR data collection at 48SU4396 (below). This GPR transect passes over an area of disturbed soil and excavation spoil. This disturbed area contains archaeological features discovered during mechanical scraping and is referred to in the data exploration tool as Tarped Area B. Excavation spoil and disturbed soils are a source of signal clutter, as are the ridges and furrows caused by mechanical scraping that are visible in this video.
Click this link to view a pop-up window displaying additional photos of 48SU4396 and a description of the survey methods.
Photos and a description of the survey strategy at 48SU2229 can be viewed here.
general slideshow of photos taken during the project (below)
