Black first encountered Angel Mounds, a Mississippian (A.D. 1050–1450) community near present-day Evansville, Indiana, in 1931, when it was one of the sites that he visited during a tour of Indiana's archeological sites. The Indiana Historical Society bought the Angel site in 1938 with funding from Eli Lilly. The archaeological site, which was in danger of being incorporated into the City of Evansville, was acquired to protect and preserve it for future research and education. Black thought that Angel Mounds would provide an opportunity to conduct a long-term study of a single archaeological site. By 1939, Glenn and Ida Black had moved into a house on the property. From 1939 to 1964, Black devoted more than two decades of study at the Angel site, beginning with a large crew of Works Projects Administration workers prior to World War II. Students participating in field course work continued excavation during the summer months after the war. Excavation was still underway when Black died unexpectedly in 1964.