DATING DRIVELINES WITH OPTICALLY STIMULATED LUMINESCENCE TO DETERMINE THE TIMELINE OF SITE CONSTRUCTION OF THE WIGGINS FORK BISON JUMP COMPLEX

The valley of the Wiggins Fork, a tributary of the Wind River in northwestern Wyoming, is lined with Pleistocene terraces hosting cairns that form an extensive network of drivelines and seven interpreted bison jumps. These archaeological features comprise the Wiggins Fork Bison Jump Complex, used prehistorically by Native Americans as a method of bison procurement. The previous age control for the site does not come from the drivelines themselves, but from a bone bed at the base of Jump #4. Radiocarbon dates from interbedded bone and charcoal layers separated by flood-sediment packages suggest multiple jump events in quick succession during ~1400-1600 AD. Bone deposits are not preserved at the base of the other jumps, likely due to erosion of the Wiggins Fork floodplain, onto which many of the jumps terminate. The spatial distribution and varying degrees of cairn degradation throughout the entire complex suggest that site utilization extended for centuries to millennia prior to the radiocarbon dates collected from the bone beds at the base of Jump #4.

Each bison jump consists of converging drivelines that form a funnel at the precipice of a slope or escarpment. The eastern limb of the funnel leading to Jump #4 displays up to four parallel drivelines extending along the terrace tread. Portions of the drivelines are dissected by gullies, and cairns closest to the terrace riser appear to be eroding into the gullies. This placement of cairns suggest that the drivelines were reconstructed further inland over time to avoid headward gully erosion which would have offered bison a quick escape when being driven to the jump.

To provide the timeline of cairn construction, this project utilizes optically stimulated luminescence (OSL) to date the sediment directly underneath rocks comprising cairns, providing placement ages for cairns. Single-grain OSL data collected from the parallel drivelines associated with Jump #4 suggests older cairn construction ages closer to the terrace riser and younger cairn construction ages as you move further inland, producing ages between ~300-800 years. This supports the hypothesis of successively inward driveline construction and long-duration utilization of the hunting complex, with the most recent use associated with the dated bone deposit at the base of Jump #4.