Geoarchaeology of the Burntwood Creek Rockshelter (14RW418), Northwest Kansas

The Burntwood Creek Rockshelter (site 14RW418) in northwestern Kansas is a large, amphitheater-shaped alcove formed in the Ogallala Formation, a late Miocene/Pliocene-age lithostratigraphic unit underlying the High Plains surface. In western Kansas, this unit consists of carbonate-cemented alluvium, and the Ogallala "caprock" forms the overhang of the Burntwood shelter. Recent archaeological excavations exposed a 3 m-thick package of late Quaternary alluvial and colluvial deposits in front of the shelter. Near the back of the shelter, three buried soils are developed in the upper 1.5 m of colluvium. The processes of rockshelter formation are ascertained through (1) description of the soils and sediments, (2) analysis of the geometry of sedimentary units, (3) grain-size analysis, and (4) thin-section analysis of a carbonate mass. Stable carbon isotope and phytolith data are used to reconstruct late-Quaternary paleoenvironments, and to explore prehistoric Native American subsistence strategies. Results indicate the rockshelter formed by groundwater sapping, and that a complex plant community existed in and around the rockshelter, and changed in composition during the late Holocene. Also, rockshelter deposits contain stratified Late Plains Archaic and possibly Late Paleoindian cultural materials, including chipped stone, bison elements, and many fragments of bison- and deer-size bone. Five ¹⁴C radiocarbon ages determined on charcoal between 1 and 2 m below surface range from 2205±20 to 2315±15 yr B.P. (uncalibrated). These dates suggest repeated use of the rockshelter during the late Holocene by Late Plains Archaic people. A concentration of Hackberry seed and fruit phytoliths in these cultural horizons may represent use for food and/or burning. A chipped stone assemblage from the lower 50 cm of the shelter fill may represent a Late Paleoindian component (Allen technological complex). This study has implications for understanding rockshelter formation in the High Plains and the activities of prehistoric Native Americans.