BEAVER DAM SITE
Anyone living on the southern plains knows how variable the weather can be from year to year (and day to day). However, modern variability pales before that which characterizes the region on centennial and millennial time scales. The Dust Bowl core of western Oklahoma and the Texas Panhandle was desert for nearly four thousand years during the long Altithermal drought of 5000 B.C. to A.D. 1200. The region has been prairie since that time, but its climate has remained highly unstable. The wettest period since the Altithermal occurred during the first Christian millennium. The deep, organic-rich Copan soil formed under the lush vegetation of this time period on the southern plains. Subsequent research has shown that climate varied on a century scale within this overall wetter pattern during the first millennium A.D. and that the Copan soil actually welds three distinct soils, the Finch Canyon (50 B.C. to A.D.100), Herring Creek ( 400 to A.D. 600), and Higgins Creek ( A.D. 775 to 1000).
In three field seasons from 1988 to 1990 members of the Oklahoma Anthropological Society excavated the Beaver Dam Site (34RM208), a stratified campsite of the first millennium A.D. on Brokenleg Creek, a spring-fed tributary of the Washita River in Roger Mills County. The site was a palimpsest of temporary camps in the Brokenleg Canyon bottom, all likely occupied during the winter when this setting provides protection from the sometimes frigid winds of the season. Three stratigraphically distinct sets of occupations were apparent at Beaver Dam. The earliest was a Late Archaic campsite associated with the large, corner-notched dart points found at multiple bison kill sites in the region. A burial associated in component contained a lunate stone, a distinctive type of boatstone found in Late Archaic contexts in an area ranging from within fifty miles of the Caprock Escarpment in West Texas south to the Colorado River. Five radiocarbon dates for this component and two nearby campsites with identical diagnostic artifacts indicate occupation during the first century A.D. Smaller corner- and side-notched dart points and corner-notched arrow points marked the second occupation and date to A.D. 400 to 600. The uppermost campsite at Beaver Dam contained no dart points, only corner-notched arrow points and sherds of a thick, cord-marked pottery that dated to A. D. 950 to 1000.
Beaver Dam was just one of many campsites concentrated along the Ogallala Ecotone, a major north-south ecological boundary in western Oklahoma associated with the eastern edge of the Tertiary Ogallala Formation. Some 60 percent of the campsites along this ecotone were of Late Archaic/Woodland (first millennium A.D.) age and cultural affiliation. The people who created the sites were living as hunter-gatherers, hunting and trapping wild game and collecting wild plant foods. Camps along the Ogallala Ecotone provided ready and efficient access to the very different plant and animal communities on either side of this boundary. Note that the three sets of first millennium A.D. occupations at Beaver Dam and other nearby sites occurred at the same time that the Finch Canyon, Herring Creek, and Higgins Creek soils were forming. These organic-rich topsoils reflected periods of maximal precipitation termed pluvials. The contemporaneity of the camps with periods of dark topsoil formation indicate use of this upland environment during the rainiest parts of the first millennium A.D., when the vegetation would have been relatively lush.
BIBLIOGRAPHY: C. Reid Ferring, The Late Holocene Prehistory of Delaware Canyon (Denton, Tex.: North Texas State University, Institute of Applied Sciences, 1982). Stephen A. Hall, "Channel Trenching and Climatic Change in the Southern U.S. Great Plains," Geology 18 (April 1990). J. Peter Thurmond, "A Late Archaic/Woodland Lunate Stone Burial in Far Western Oklahoma," Bulletin of the Texas Archeological Society 60 (1991). J. Peter Thurmond, "Archeology of the Dempsey Divide, a Late Archaic/Woodland Hotspot on the Southern Plains," Bulletin of the Oklahoma Anthropological Society 39 (1991). J. Peter Thurmond, Craig C. Freeman, et al., "Preliminary Report of an Ethnobotanical Survey along the Ogallala Ecotone on the Dempsey Divide in Roger Mills County, Oklahoma," Oklahoma Archeology 50 (2002).
John Peter Thurmond
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