Archaeo-Physics, LLC - geophysical survey and subsurface mapping

2008 and 2009 Texas Archaeological Society Field Program

Geophysical investigations at three Middle Ceramic period sites in NW Texas

Courson Oil & Gas of Perryton, Texas sponsored geophysical investigations at three archaeological sites in advance of the upcoming 2008 and 2009 TAS field programs. The results from these surveys will be used to guide placement of excavation blocks during the TAS fieldwork. The sites are Middle Ceramic period settlements located in the Canadian River Valley of the Texas panhandle. Although only limited testing has been conducted, preliminary results suggest they are Antelope Creek phase permanent habitation sites. The names of the sites are Chill Hill, Eastview, and the McGarraugh Ranch site.

The investigation utilized two primary geophysical methods: magnetic field gradient and electrical resistance survey. Chill Hill was also investigated with a third geophysical technique known as electromagnetic conductivity survey. Results are presented below via an interactive data analysis tool. The analysis tool allows the viewer to examine several different displays of each data set. For example, it is possible to view the magnetic survey results as low, medium, or high contrast images. This allows the viewer to understand changes in relative signal strength, as well as see extremely subtle detail that would not otherwise be visible. The positive and negative components of the magnetic signal are also separated and displayed independently. This facilates visualization of extremely subtle patterning. In all of the magnetic images strong positive values are depicted in black, while strong negative values are depicted in white

The resistance and EM data are presented both as standard plots and after the application of a processing technique known as high-pass filtering (HP filtering). HP filtering is a background removal filter used to suppress large-scale geologic variation and to enhance small low-contrast anomalies. In some cases color plots are used to enhance characteristics of the data.

The interpretations offered here may be considered initial hypotheses. These hypotheses will be tested during the upcoming TAS field program. Please check back in the fall of 2008 to view testing results!

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Survey Results

The geophysical investigations identified interesting anomalies and complex patterning at each of the three sites. Although the signal response is often exceedingly subtle, these anomalies are thought to represent buried archaeological features, structures, and/or large-scale landscape modifications associated with the occupation of the site. The TAS field program will systematically test these anomalies via a variety of methods including soil coring, shovel tests, test trenches, and large block excavations. The results of this testing program will be presented on this web page as they become available.

The Chill Hill site is a recently discovered Middle Ceramic settlement is located in the Canadian River valley of the Texas Panhandle. The site is extremely large, encompassing approximately 600,000 square meters, making it perhaps the largest prehistoric settlement found in the Canadian River valley during the last 70 years. The site is buried beneath 30 to 40 cm of aelian deposits, resulting in a very low-contrast geophysical signal response. The site was detected while conducting a pedestrian survey for a proposed gas well location. The latter was moved 50 meters to the northeast to avoid impacting the site.

Besides its large size, Chill Hill is also noteworthy in terms of the total quantities of artifacts present on the ground surface. Cultural materials from the settlement are typical of other Middle Ceramic sites of the Canadian River valley and include cordmarked ceramics, chipped stone tools, cores, and debitage, bone tools, faunal debris, fire altered rock, mussel shell fragments and tools, ash, charcoal, and groundstone. This site is also unique for the frequencies of Eastern Pueblo trade items found here. To date, nearly 90 pieces of obsidian, including three arrow points, and ten Olivella shell beads have been recovered from the site. X-ray fluorescence analysis has identified the source of the obsidian to be Cerro Toledo, which is located NW of Santa Fe in New Mexico.

A magnetic field gradient survey was completed over 19,000 square meters of the settlement, with smaller portions of the site investigated by electrical resistance and EM Conductivity survey. Although the magnetic survey area was extensive, it covered only about 3% of this unusually large site.

The geophysical investigation has identified dozens of interesting anomalies that may represent buried features, structures, and/or large-scale cultural landscape patterning. Some of the more interesting anomalies include linear induced magnetic lows with high electrical resistance correlates. Patterned signal with these characteristics may represent stone walls constructed from low susceptibility caliche, or possibly ditches, foot trails, or "blow outs" around the edge of structures that have filled in with relatively non-magnetic aeolian deposits. Several strong bipolar magnetic anomalies appear to represent fire-altered features, perhaps portions of structures that have been burned, or other features containing significant amounts of burned materials.

The McGarraugh Ranch site (41RB1) is a large Antelope Creek phase permanent habitation site.  It is approximately 500 x 200 m in size.  Cultural features present at the site include residential structures, some with stone foundations, storage facilities, hearths, and middens.  The cultural assemblage at the site is typical of Antelope Creek phase sites and includes some exotic trade items, notably obsidian, from the Eastern Pueblos of New Mexico.  Beyond our geophysical survey, no formal archaeological investigations have been undertaken at the site.  Regrettably, considerable pothunting has occurred at the site. Geophysical survey was conducted over a 60 x 60 m block located near the center of the site. The survey covered approximately 4% of the total site area.

The results from the McGarraugh Ranch site are dominated by large scale patterning in the electrical resistance data that create unusual geometric patterns. This patterning may be described as two concentric bands around a "central" circular anomaly that is most clearly defined in the magnetic survey data.

The Eastview site is a permanent settlement of Middle Ceramic period age situated atop a high upland remnant approximately 4 km upstream from Chill Hill. As such, the site provides a commanding view in all directions. Along the southern and central portions of the site there are three alignments of caliche stone slabs laid on edge that may represent the walls of residential structures. Complex patterning in the magnetic survey results suggest there are numerous additional buried features and/or structures. The magnetic field gradient survey was conducted over 4500 square meters of the site, encompassing nearly 100% of this small settlement. Soil resistance survey has not been conducted at this site.

The 2008-2009 TAS Field Program

The 2008-2009 TAS field program will be test both the Chill Hill and Eastview sites, as well as several additional prehistoric and historic archaeological sites. In 2008 more than 480 volunteers took part, making this perhaps the largest single archaeological field program in American history. A brief photo slideshow from the 2008 season can be viewed below. The 2009 program is scheduled for 13-20 June. After completion of this seasons excavation results a planview map of mapped features will be compared with the geophysical anomalies discussed above.

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