Total station and GPS methodologies aid surface mapping of archaeological site.

Ongoing research endeavors on private lands in Dove Creek, Colo., and a recently worked site known as Mitchell Springs Archaeological Complex overseen by the Mitchell Springs Ruin Group have provided a unique opportunity for research collaboration between archaeologists, anthropologists, geographers and geophysicists. Having been only slightly to moderately disturbed, the Dove Creek Ruins and Mitchell Springs sites exemplify the efforts of owners to investigate the history of what lies beneath the surface, while maintaining and preserving the major portion of the site. Non-invasive mapping and geophysical exploration methodologies, including the use of surveying accurate GPS and total station instrumentation, have allowed recognition of surface and subsurface structures with little or no disturbance to the sites, thereby preserving such features for later generations.

These prehistoric communities represent the re-mains of a group of the Anasazi Indian culture that inhabited the Colorado Plateau area of the southwestern United States between the years of A.D. 900 and A.D. 1000. The importance of these vestiges lies in the fact that they represent a little studied era in the prehistory of the people of the Four Corners area of southern Utah, southwestern Colorado, northwestern New Mexico and northern Arizona. The ruins provide a wealth of opportunity for both undergraduate and graduate student research.

The establishment of accurate horizontal and vertical control, detailed site topography, placement of excavation units and mapping of artifacts are all fundamental tasks on a working archaeology site. Mapping at the centimeter level as materials are uncovered allows archaeologists to reconstruct the exact placement and orientation of artifacts on more accurately detailed maps post-excavation. In addition to natural geomorphology, distribution of ceramics, stone implements, faunal and human remains, and the mapping of surface disturbances play an integral part of studying such areas.

At the Mitchell Springs and Dove Creek Ruins sites, a Leica SR530 Geodetic RTK receiver and base station were used to establish Universal Transverse Mercator (UTM) 12 grid coordinates at onsite monuments using static observations of at least four hours' duration during a window of low GDOP (geometric dilution of precision, a measure of the geometrical "strength of figure" of visible satellites) and high satellite visibility. Raw GPS data sent through the National Geodetic Survey's Internet-based OPUS (Online Positioning User Service) was processed and received. GPS point data included topography, creeks, roads and paths, fence lines, archaeological structures and artifacts mapped at survey grade accuracy (one to two centimeters horizontally). The GPS control allowed workers to survey on the UTM Zone 12 North Grid using a Sokkia Set 4BII total station rather than using an arbitrarily established grid. The total station, used as a supplement to the acquisition of GPS point data, permitted rapid acquisition of points using multiple rods and prisms with three to four survey crew members and one total station operator at closely spaced intervals of no more than 3 m, covering an area of 160 acres (1/4 section). Although mapping at the site is not nearly complete, the 2003 and 2004 field seasons resulted in the acquisition of 2,557 total station points and 4,263 GPS points at the Dove Creek Ruins site alone.

Rectangular grids staked out in areas of potential archaeological interest were established for geophysical exploration. Multiple subsurface imaging methods, including magnetic gradiometry, electron magnetic induction, resistivity and ground penetrating radar were used to help survey these areas and to test the usefulness of non-invasive geophysical methods for mapping suspected ruins prior to archaeological excavation. Interpretation of contour maps and digital images produced from these data provided valuable insight into the archaeological information located in the shallow subsurface and were useful in guiding subsequent excavation efforts during summer field schools. Field verification of certain geophysical anomalies by archaeological teams identified a pueblo with connecting rooms, several deep storage pits and three burials. Using multiple geophysical methods along with careful data processing increases the possibility of locating subsurface archaeological features.

The Dove Creek Ruins topography helped to exemplify minor surface depressions characteristic of buried ceremonial structures known as "kivas." These ancient ceremonial structures were constructed using carved sandstone blocks from the near-surface and outcropping sandstone (sandstone exposed at the surface). Small topographic ridges, typically along the north rim of the kivas, revealed block structures (small living quarters and storage areas) as de-fined by the topographic surveys. As many as 20 possible kiva structures on a single ridge line, and an additional great-kiva on an adjacent ridge, were discovered during the 2004 field survey. These areas clearly are favorable for future excavation. These data were then used to define areas of geophysical exploration to further refine areas of possible excavation in preparation for the 2005 field season. Following geophysical exploration at Mitchell Springs Ruin in 2001, excavation within the grids exposed wall structures, storage pits and kiva walls, which were mapped using the Leica SR530. Having only partially disturbed the study areas, care is taken to reintroduce the soils excavated to allow for re-excavation in future studies. The areas will continue to be excavated over the next few field seasons until further exploration is required.

Without the aid of geophysical exploration, supported by surface mapping using total station and GPS methodologies, finding these features beneath the substrate without randomly excavating would be nearly impossible. As with many academic projects, funding for such research is virtually nonexistent. All participants in these projects during the last four years have volunteered their expertise and their equipment at no cost in the general interest of archaeology, geology, geography and geophysics. It is what scientists do; that is, further not only their knowledge of the earth sciences, but propagate the education of many students who have enthusiastically participated over the years.

All surveying equipment for this project was provided by Kara Company, Countryside, Ill., whose guidance and generous support has made possible this and other scholastic endeavors over the years.

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Manufacturer and Technical Information:

Leica Geosystems: www.leica-geosystems.com
Sokkia: www.sokkia.com
National Geodetic Survey: www.ngs.noaa.gov/OPUS