Sentinel Butte: neutron activation analysis of White River Group chert from a primary source and artifacts from a Clovis cache in North Dakota, USA

Instrumental neutron activation analysis (INAA) was used to characterize the chemical composition of chert from a primary source in western North Dakota. Known as Sentinel Butte, this source is part of the Eocene-age White River Group (WRG), a widespread geological formation on the central and northern Plains. INAA results demonstrate that it is chemically distinct from other known chert-bearing WRG. Further, analysis of three bifaces from the nearby Beach Clovis cache site demonstrates that they are made of chert from Sentinel Butte, and most likely the other 55 White River Group Silicate (WRGS) bifaces in the cache are as well. Although Clovis caches typically are dominated by materials transported hundreds of kilometers, it is argued that the advance manufacture and caching of bifaces even a short distance from a source may be a highly effective tactic to reduce gearing up time and hence search costs associated with the pursuit of mobile game at the close of the Pleistocene.