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Abstracts/Summaries:

Electromagnetic surveys are fast method of locating and mapping some large earth features such as leveled mounds and refilled ditches. They can be a substitute for resistivity surveys and are particularly suitable where the surface soil is dry, hard, or rocky, or where the vegetation is moderately dense. As in all geophysical techniques, it is necessary that the features to be located are sufficiently different from the surrounding terrain. Results from three sites will illustrate the capabilities of electromagnetic surveys. Fort de Chartres is an 18th century French fort built next to the Mississippi River in llliniois. An excavation trench along a curtain wall of this fort revealed the location of a fortification ditch; this fortification had been long ago filled in with rock rubble and earth. An electromagnetic survey was carried out adjacent to the excavation. A band of high conductivity probably indicates the extension of the fortification ditch parallel to the curtain wall of the fort and about 7 m from it. Electrical tests indicate that this band is caused by high conductivity material in the soil directly below the bottom of the refilled ditch, possibly resulting from chemicals that have seeped through the bottom of it. The refill material within the ditch is actually low in conductivity, as is to he expected, since much of this material is probably stone. The soil around the ditch has a high content of clay. Used with permission.

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New Techniques of ground-penetrating radar (GPR) acquisition and computer processing were tested at archaeological sites in the American Southwest and found to be highly effective in producing images of buried archaeological features. These new methods, especially amplitude slice-maps, were combined with more standard data processing and interpretation techniques and tested at sites with little or no surface expression. In southern Arizona, numerous pit structures buried in terrace alluvium were discovered and mapped. In the Four Corners region, a Chaco period great kiva and other pit structures and features were mapped by GPR and later confirmed through excavation. At some sites, GPR surveys did not successfully identify buried archaeological features. These failed surveys highlight both geological and methodological problems including soil conditions, surface disturbance, and equipment calibration that may be avoided or ameliorated in furture GPR surveys. Used with permission.

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Portable proton magnetometers were employed at a number of sites dating to the Archaic and Late Prehistoric periods at several different localities in NW and west-central Texas in an attempt to locate subsurface prehistoric features for excavation. Eight magnetic surveys were performed, resulting in the identification and recovery of several fired features, clusters of ceramics, and numerous metal objects of historical age. The results demonstrate that thermoremanent magnetization of fired artifacts and features in this environment is often strong enough to allow their detection by magnetic prospection, and suggest that this technique is a valuable approach for maximizing data recovery during testing and mitigation of shallowly-buried alluvial sites in the region. Negative results, however, do not necessarily mean that features are absent; therefore, the method should be considered an adjunct to, rather than a substitute for, traditional testing procedures.

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Throughout the 17th century, Santa Catalina de Guale served as the northern outpost of Spanish colonization along the Atlantic seaboard. Abandoned in 1680 and lost in the forests of St. Catherines Island, the mission site was relocated 300 years later by a systematic proton magnetometer survey. Analysis of magnetic data was greatly enhanced by the use of several computer graphic formats. The results of the survey, analysis, computer graphic production, and test excavations are presented.

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A Controlled Archaeological Test Site (CATS) facility has been constructed in Champaign, Illinois, by the Cultural Resources Research Center at the U.S. Army Corps of Engineers Construction Engineering Research Laboratory, with funding provided by the National Center for Preservation Technology and Training. The test site will be utilized for research and training with geophysical applications in archeology. The CATS facility replicates a range of archeological features commonly encountered in North American archaeological sites and offers a controlled envieronment for the application of non-destructive investigative techniques. The site provides the opportunity for geophysicists and archaeologists to work with features of known geophysical attributes in a controlled geomorphological setting. In addition to providing a controlled "test bed" for training students in the use of geophysical techniques, the CATS facility will be available for research in a broad range of problems associated with archaeogeophysics, such as the effects of environmental conditions on geophysical expression, sensor type and configuration, data sample density, image processing and pattern recognition, operator variation, and feature variability. The research will contribute to our ability to interpret geophysical data and refine field methods for application in archaeological investigations. Used with permission.

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Despite claims that ancient Maya canals are found throughout the central Maya Lowlands, our study of satellite and aircraft imagery indicates that canals are concentrated in three regions: northern Belize, southern Quintana Roo, Mexico, and along the upper Candelaria River and its tributaries in Campedche, Mexico. Earlier reports of lattices of small canals in the karstic depressions, or bajos, of Peten, Guatemala, based on the analysis of airborne radar imagery, have not been verified with other remote sensing data or by field research. Our analyses of this same airborne imagery and Seasat satellinte radar imagery demonstrate that the spatial resolution of, and speckle noise in, existing radar imagery make it inadequate for mapping lattice patterns of small canals. Radar imagery and Landsat Thermatic Mapper imagery were, however, useful in mapping large canals, which in most cases are connected to lattices of smaller canals. Furthermore, our analyses of wetland soils, vegetation, and hydrology confirm that canals are confined mostly to perennially moist wetlands where the water table lies near the surface in the dry season. The seasonal swamps typical of the karstic depressions in the vast interior portion of the Maya Lowlands do not contain canals; here, frequent inundation plus severe desication during dry period would have made cultivation difficult and unreliable. We conclude that the majority of densely-populated Classic Maya sites were not dependent on wetland agriculture. Used with permission.

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An electrical resistivity survey and accompanying soil analyses were performed over an exposed but unexcavated prehistoric house in Peoria loess in west-central Illinois. Positive resistivity anomalies occur along the trenches for the house walls and within the house and distinctive patterns in contoured resistivity data occur over the house. Soil analyses show that quartz, kaolinite, montmorillonite, illite, and hematite are the main mineral constituents in the soil. Within the house basin, the soil is dark gray in color because of the presence of organic carbon. Prominent positive electrical resisitivity anomalies occur where the dark soil is thickest. Analyses of the resistivity and soil data enable the identification of several anthropogenic features within the house and suggest that electrical resistivity data would be helpful to archaeologists in doing both detailed and reconnaissance work. For example, the mean amplitude and fabric patterns in contoured resistivity are distinctive over the house relative to areas outside the house. This fact suggests that similar analyses of reconnaissance resistivity data might be helpful in exploration for large archaeologic activity areas such as whole villages or camps. Also, detailed analyses of the resistivity and soil data, in conjunction with information already available from other excavated structures at Orendorf village, suggest that the electrical resistivity technique can serve as a valuable, but ancillary, tool to help archaeologists focus their efforts and decide which of the many structures in a village should be excavated.

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A survey of Valley Forge National Historical Park was carried out by MASCA in 1978 for the National Park Service utilizing, among other techniques, aerial photography, the cesium magnetometer, and ground penetrating radar. The aim of the project was to locate evidnece of the encampment of 1777-78, using for the most part non-destructive methods. Hut sites and offal pits dating from the Revolutionary War period were identified and a comprehensive survey of previous archaeological work at Valley Forge was carried out. A major problem in interpreting the data from the various techniques employed was the amount of modern distrubance at the park, mostly dating from the three Boy Scout Jamborees held there in 1950, 1957, and 1964. Despite these problems, valuable information about the Revolutionary War remains was recovered, and a comprehensive plan for future research was formulated.

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A recent rebuttal in the Journal of Field Archaeology by Adams and others takes issue with our analysis of remote sensing imagery and ecological data from which we concluded that: 1) their previous analysis of radar imagery was in error, and 2) there are no large ancient canal systems in the seasonal swamps of the interior Maya lowlands. We stand by our original interpretations and conclude that their rebuttal reflects a lack of understanding of radar imagery, remote sensing verification, and Maya wetland hydrology and soils. We also conclude that our opposing interpretations are in part the result of different approaches: theirs based on the development of an ancient Maya agriculture paradigm and ours on hypothesis testing. Used with permission.

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A soil resistivity survey of the "Central Building Complex" at Puerto Real, a 16th-century Spanish town on the north coast of Haiti, was conducted during the 1980 summer field season. Soil resistance was measured over an area of ca. one acre, with readings taken at 1-m intervals. The resultant data enabled the construction of resistivity contour maps (showing areas of higher and lower resistance) that were available as fieldwork progressed. The maps enabled quite accurate prediction of subsurface feature locations, and thus were a valuable tool for the efficient use of limited excavation time. Used with permission.

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The authors have conducted site tests of the self-potential (electrical field conductivity) method in the Harpers Ferry, Ft. Washington, and Piscataway historic sites on the Potomac River shore of Maryland. The tests were successful in identiying buried structures as well as soils disturbed in historical times. The authors also note that recent rainfall, superficial variations in soil composition (chemistry), and polarization of electrodes can skew SP voltages. The tests are quick and are the cheapest of all geophysical exploration methods. The primary difficulty is in obtaining well-trained personnel to operate the system, as well as analyzing the products. Used with permission.