USING LUMINESCENCE DATING TO INVESTIGATE GEOMORPHIC AND ARCHAEOLOGIC FEATURES AT THE WIGGINS FORK BISON JUMP COMPLEX, NORTHWESTERN WYOMING

The valley of the Wiggins Fork, a tributary of the Wind River in northwestern Wyoming, contains Pleistocene terraces that thousands of cairns that form an extensive network of interconnected drivelines and at least 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. Prior age control for the hunting complex came from a bone bed at the base of one of the jumps, titled Jump #4. Radiocarbon dates from interbedded bone and charcoal layers separated by flood-sediment packages suggest multiple jump events in quick succession around ~1400-1600 AD. 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, in which the cairns appear to collapse into. This cairn placement suggests that the drivelines were reconstructed further inland to avoid headward gully erosion that may have offered bison an escape when being driven to the jump.

This research utilized optically stimulated luminescence (OSL) to date the sediment directly underneath rocks comprising cairns and associated alluvial features, providing placement ages for cairns and geomorphic context. Single-grain OSL results from Jump #4 suggest that the jump funnel was constructed during or slightly before the successful use of the jump. Single-grain OSL results from the parallel drivelines that approach Jump #4 revealed that the drivelines were constructed between ~300 to 800 years ago. A slight decrease in age as the drivelines move further from the terrace riser represents a long-term investment in the landscape and adaptation to geomorphic change.