Geophysical Capabilities and Research

For a few years now, TARL has had an excellent magnetometer and we have used it on several sites in various parts of Texas as well as in Colorado and New Mexico. We also have a ground penetrating radar with two antennas for different depth capability. This past year, with funding provided by the College of Liberal Arts, we have acquired a GPS unit with sub-meter precision capability for use with our magnetometer, as well as a new electrical resistivity unit. With this array of equipment, we now have a substantial capability for near-surface geophysical sensing in archeological contexts.

In April, Dale Hudler and students in his Digital Data Systems in Archaeology class conducted a magnetometer survey of much of site 41GL189, a burned rock midden site in western Gillespie County. Part of the site was also surveyed with our ground penetrating radar and all of the site was mapped with a total data station. In part, this site was chosen for magnetometer survey because the two known burned rock middens there appear to be in a different geological context than other burned rock middens we have worked on in Menard and Kerr counties. In addition to the mapping and geophysical surveying at this site, a number of holes were dug with a posthole digger in an effort to collect subsurface data for use in interpreting the geophysical data. Additional work on all of these tasks is needed before a report can be prepared.

As we have been building our geophysical sensing capabilities, we have been attempting to use our equipment at different types of sites; and we had been looking for a good opportunity to use our magnetometer on an adobe pueblo in the El Paso area. We got that opportunity in the fall of 2005 at two sites on Fort Bliss that had been cleared of mesquite and the other woody vegetation during a testing program by Geo-Marine. At one of these sites, the upper walls of an adobe pueblo were made visible by the clearing, so we had an outstanding opportunity to learn what an adobe roomblock looks like when surveyed with a magnetometer. In addition to seeing the known architecture, we may have better defined another roomblock already known at the site. Some other anomalies may represent pitstructures and other types of features. Lastly, in December, Dale Hudler and Jonathon Jarvis conducted a magnetometer survey of the portion of the A.C. Saunders site (41AN19) in Anderson County owned by the Archaeological Conservancy. Saunders is best known as a late prehistoric Caddo “perpetual fire” site on the basis of 1930s excavations by A.T. Jackson and his UT crew. The most prominent feature on the site is a large ash mound about half of which is on Conservancy property. More than 18,000 square meters was surveyed with the magnetometer at Saunders, all of it in a portion of the site heretofore basically unknown archeologically. The magnetometer found a number of anomalies, some of which may represent Caddo structures; but none was nearly so well defined as those we found previously at the George C. Davis site (Caddoan Mounds State Historic Site) in adjacent Cherokee County.

In 2006, a major geophysical sensing effort will be devoted to site 41VT141 in Victoria County where Michael Bever will teach the Department of Anthropology’s summer field school. A primary objective is to define the stratigraphy of the site. There is a dense clay deposit in the site, as much as three meters below the surface, upon which may be a late Paleoindian component.