The Colorado Study Area: Background

Between 1988 and 1996 multiple surface scatters of chipped stone, containing in excess of 27,0000 artifacts, have been mapped in a remote and arid region on the Colorado Plateau, near Grand Junction, Colorado. The area mapped is a contiguous region of approximately six hectares (Figure 1). The remoteness of the project area, caused by a paucity of access roads and difficult-to-cross canyons, has guaranteed a remarkable surface record of relatively undisturbed debitage scatters, reflected by the presence, yet, of roughly 1,200 chipped and ground stone tools, including nearly 100 projectile points. Other advantages of this study area are its general lack of dense vegetation which allows a high level of surface visibility, a situation of soil deflation that yields numerous surface-visible artifacts, and the presence of a large number of high-density flaking debris clusters, providing multiple "units" of study.

The apparent high density of prehistoric activity in the study area is probably explained by its location adjacent to a canyon that harbors water, riparian, and wildlife resources. The canyon varies in depth between 60-120 meters and possesses shear-sided walls, except just below the project area where the wall has collapsed. Thus, easy access to the canyon is possible only at this locus or at the canyon mouth some six kilometers distant (Figure 2).

This region of western Colorado was inhabited by hunting-and- gathering groups with surface archaeological remains consisting solely of chipped and ground stone tools and flaking debris. It is quite likely that hunting parties of the Fremont Culture traversed the area (the Fremont practiced part-time agriculture, made ceramics, and occupied settled village in nearby Utah from approximately AD 500-1300), but there is no evidence that specifically identifies their presence in the study area. Projectile points recovered by the project from the early Archaic Period suggest occupation for several millennia BC, although most point to use of the area during the past 1,500 years.

Field Methods

Given the rich nature of the surface archaeology, and a goal of exploring structure and organization within and between the various chipping debris scatters, full coverage survey methods were attempted. A grid of four meter squares was superimposed over the study region. One hundred such squares (40 x 40 m) were laid out at a time by a crew of two using a transit and meter tapes. Pin flags and large flagged nails were employed to mark grid corners. In each grid unit a survey was conducted ensuring uniform aerial coverage of the study area. "Saturation" survey methods were employed in each grid to eliminate discovery biases. As a start-point, only those artifacts greater than five millimeters in size were considered to allow greater uniformity in the recorded data. Each grid was inspected by a two-person crew. The team began in opposite corners of a square with each person walking four one-meter-wide transects. This process was then repeated a second time with transects in an orthogonal direction. As a consequence, each square was surveyed four times with one meter transects and any locus was viewed from four different directions. The end result was "total coverage" survey where few artifacts were overlooked (repeat surveys verified this to be the case; Figure 3).

Effects of vegetation patterns on surface mapping

A small part of the data at full resolution (point-plotted) are illustrated in Figure 4, which also maps the significant vegetation. It is clear that intensive and varied flaking activity did occur in this mapped region, much of it was localized, and that vegetation does affect results at this scale. The collapsing of the data into 4 m squares (see below) may actually enhance the overall pattern by generalizing it. More complete and detailed quantitative analysis of these data is currently underway.

Debitage Sorting

One focus of research using these data has been on the spatial properties of the mass debitage. This research has shown that in many of the many scatters, a subtle spatial sorting tends to occur based largely on debitage size. For any size class of debitage, the absolute counts tend to be greatest at the flaking cluster centers. However, when the size class counts are expressed as proportions of total debitage per 4 m grid square it becomes apparent that somewhat greater proportions of large debitage pieces occur along scatter margins while the reverse happens for small-size debitage (Figure 5). This is simply the result of the physical processes associated with percussion-based knapping, which cause large flakes to have a somewhat higher probability of travelling farther from the knapping locus than small flakes (due to the requisite stronger blows), a process that has been verified through experimental knapping.

Evidence of "Toss Circles"

One clear pattern observed in the data is rings of cores that surround many of the debitage concentrations (Figure 6). It might be tempting to explain the ring pattern as resulting from down-slope movement of these large and generally round objects. Nearly all of the flaking concentrations occur on the ridge crests of the study area (Figure 1). While some cores do occur down-slope, and quite likely have migrated down- slope through time, as many occur along cluster margins on ridge crests and even up-ridge of the flaking centers. The most plausible explanation of the core distribution lies in the phenomenon documented by Binford: that of "toss circles." Assuming one or more knappers working stone near the locus of a scatter center, as cores were spent they probably were simply tossed over shoulders, or perhaps kicked aside, causing the ring phenomenon.

Tool Distributions

The numerous tool types illustrate various distributions and and the presence or absence of spatial associations (two are shown in Figure 7). One interesting characteristic of the ground stone is a significant correlation with mild slopes, immediately off the ridge crest, which perhaps facilitated the grinding process. Projectile point distributions (not pictured) give temporal indications to many of the activity areas.

A Magnetic Survey for Hearths

The locus of hearth features with respect to chipping stations and activity areas may yield clues about site structure and organization. In 1997, 8,000 m² of the mapped area was surveyed by a magnetic gradiometer at a sampling density or two measurements per meter. Two anomalies were encountered that may represent prehistoric hearths. See the magnetic survey results.

Project Bibliography (by K. L. Kvamme)

(1998). Spatial Structure in Mass Debitage Scatters. In Surface Archaeology, A.P. Sullivan III, ed., University of New Mexico Press, Albuquerque, pp. 127-141.

(1998). Final Report: Magnetic Gradiometry Survey at 5ME6489, Mesa County, Colorado, 1997. Prepared for Bureau of Land Management, Grand Junction District, Colorado.

(1996). Investigating Chipping Debris Scatters: GIS as an Analytical Engine. In New Methods, Old Problems: Geographic Information Systems in Modern Archaeological Research, Herbert D. G. Maschner, ed., Center for Archaeological Investigations, Occasional Paper No. 23, Southern Illinois University, Carbondale, pp. 38-71.

(1995). Final Report: High Resolution Cultural Resource Mapping Project at Sieber Canyon, Mesa County, Colorado, 1994 Season. Prepared for Bureau of Land Management, Grand Junction District, Colorado.

(1993). Spatial Statistics and GIS: An Integrated Approach. In Computing the Past: Computer Applications and Quantitative Methods in Archaeology, CAA92, J. Andresen, T. Madsen and I. Scollar, eds., Aarhus University Press, Aarhus, Denmark, pp. 91- 103.

(1992). Geographic Information Systems and Archaeology. In Computer Applications and Quantitative Methods in Archaeology 1991, G. Lock and J. Moffett, eds., BAR International Series S577, Tempus Reparatum, Oxford, pp. 77-84.

(1990). Final Report: High Resolution Cultural Resource Mapping Project at Sieber Canyon, Mesa County, Colorado, 1989 Season. Prepared for Bureau of Land Management, Grand Junction District, Colorado.

(1989). Final Report: High Resolution Cultural Resource Mapping Project at Sieber Canyon, Mesa County, Colorado, 1988 Season. Prepared for Bureau of Land Management, Grand Junction District, Colorado.

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