NORMAN, OKLAHOMA—Leland Bement of the University of Oklahoma was surveying bison kill sites along the Beaver River in northwestern Oklahoma when he found butchered bison bones on a narrow bench of land between two arroyos. Such “arroyo traps,” where the ditches were used as natural drive lines, are the oldest-known method of large-scale bison hunting. The pieces of leg, foot, and back bones were accompanied by a quartzite hammerstone and a small flake made from Texas chert. This site is 11,500 years old, and is “the most recent Paleoindian site along this stretch of the river,” Bement told Western Digs. “All of these sites [in the Beaver River complex] are large-scale bison kills in arroyo traps. Each kill was of between 30 and 60 animals.” Taken together, the sites, which are part of a study being conducted by Kristen Carlson of the University of Oklahoma, reveal a transformation from the tools of the Clovis culture to the Folsom tradition. “To have a kill complex in use for over 800 years speaks to the ability of hunters to plan and coordinate and revisit a successful hunting ground through generations,” Carlson said. To read about the remarkable way prehistoric Native Americans hunted buffalo, go to "Letter from Montana: The Buffalo Chasers."