EXCEPTIONAL PRESERVATION OF LATE PALEOINDIAN CULTURAL MATERIAL ON A RAPIDLY AGGRADING VALLEY FLOOR, ASH HOLLOW DRAW, WESTERN NEBRASKA

Four Late-Paleoindian archaeological sites lie along a 1.4 km reach of Ash Hollow Draw in western Nebraska. Two sites (Clary Ranch and O.V. Clary) have been excavated using high-resolution techniques. The Clary Ranch site is a late summer/early fall secondary bison-processing site, while the O.V. Clary site is a residential camp.

Six lithostratigraphic units (A to F from bottom to top) have been identified along a 2km reach of Ash Hollow Draw. The Paleoindian cultural material at the Clary Ranch and O.V. Clary sites occurs within Unit E. At the O.V. Clary site Unit E consists of brown coarse silt or very fine sandy silt alternating with dark brown or very dark grayish brown silt. Unit E is horizontally-laminated with individual laminae ranging in thickness from 1.4cm to 9.6cm. As many as 30 laminae have been identified, described, and their elevations recorded with a total station across the archaeological excavation block, in a backhoe trench, and in profiles along the cutbank. We have been able to reconstruct two-dimensional and three-dimensional surfaces of the individual flood laminae across the site. In areas where cultural material is sparse, laminae tend to be more horizontal and are more readily identifiable. Laminae are contorted and difficult to identify within the area of the densest cultural material (especially in and around the hearth areas). Laminae in the backhoe trench (perpendicular to modern draw) become indistinct (merge into a massive unit) away from the active axis of deposition. The cultural material is densest along the aggrading axis of the valley floor. Particle size data reveal that occupation of the site occurred during a time of predominantly silt deposition. This was very important to preservation of the cultural material. Later, slightly higher-magnitude flooding (as revealed by percentages of sand) disturbed artifacts.

Based on the seven most consistent AMS radiocarbon ages (deemed the most reliable) at the O.V. Clary site, the laminated Unit E ranges in age from less than 9150 yr B.P. to about 9000 yr B.P. The radiocarbon ages at the O.V. Clary site for Unit E, and the bracketing ages for Unit E elsewhere within the Ash Hollow drainage, all suggest very rapid aggradation of the silt. This rapid aggradation appears to have sealed both the Clary Ranch and O.V. Clary sites quickly and helped preserve a phenomenal amount of cultural material at these sites.