An intriguing question in the prehistory of the northeastern United States and Canadian maritime is the possible overlap of Pleistocene megafauna and early humans. When did the last mastodon die? When did the first Paleoindian arrive? There is evidence from New York State’s Genesee County that a human presence at 10,810-10,990 years BP may be coeval with the presence of mastodons and other extinct fauna. Elsewhere, sites with mastodons and mammoths from Dutchess, Chemung, and Wyoming counties, dating ca. 500 years earlier, do not yet show a human presence. The Davis Site in Essex County is associated with a late Pleistocene, Champlain Sea strand line dated ca. 11,300 years BP. The effects of post-glacial sea-level rise and the inundation of earlier sites further complicates the problem. Did the first humans contribute to the extinction of the mammoth and mastodon? This question is the subject of a new series of investigations, looking at sites that share the twilight of the North American Pleistocene fauna and the dawn of humans.