The oldest traces of human presence in Quito were excavated by American archaeologist Robert E. Bell in 1960, on the slopes of the Ilaló volcano, located between the eastern valleys of Los Chillos and Tumbaco. Hunter-gatherers left tools of obsidian glass, dated to 8000 BC. This archaeological site, called "EI Inga," was brought to Robert Bell's attention by Allen Graffham. While employed as a geologist in Ecuador, Graffham pursued his amateur interest in archaeology. He made surface collections at the site during 1956. The discovery of projectile points, particularly specimens with basal fluting, stimulated his interest, and he made several visits to the site to collect surface materials. Graffham's previous interest in Paleo-Indian remains, and his experience with early man materials in Kansas and Nebraska in the Central Plains of the United States, led him to believe that the site was an important discovery.