The collection reflects his career activities and his research. The largest part of Dr. Mahan's materials consist of his subject files, which cover all aspects of his life and career. The other series are more specific to the various phases of his life. The ISAC series also contains a subject file and there is some overlap with the first subject file. The papers include correspondence, copies of articles or excerpts from longer secondary works, notes extracted from primary sources, tapes of interviews and Indian ceremonies, tapes and interviews of research trips to Mexico, India and Pakistan, and student papers. It also contains notes taken from colonial and early national period primary sources relating to the history of Eastern North American Indian tribes and early 19th century archeology; articles from periodicals and newspapers (1952-1977) relating to American pre-history, particularly discoveries of inscriptions, coins, and metal artifacts indicating pre-Columbian trans-Atlantic cultural contacts; personal correspondence (1943-1956) relating to his service in Europe in World War II, research into American Indian and Georgia history; and a card file which indexes and annotates information, dates, and bibliographies in this collection.

The Yuchi Indians represent one of the largest subject areas within the collection with publications, notes, and correspondence relating to their history, culture, ethnology, phonology, the visit to Columbus of Chief Joseph Brown (1833-1935), their Green Corn Ceremony (tape), and the Coweta Memorial Association which acquired land in Russell County, Alabama, for the Yuchi tribe. Alternative spellings of the name of the tribe include Euchee, Outchee, Uchee, Uchi or Yuchee. Other subject areas include general archaeological investigations in the region; the Bull Creek archaeological site in Columbus; the Kolomoki Indian mounds; the Singer-Moye Mounds; the Rood Mounds; the Hearn Tablet, a Sumerian tablet found in LaGrange, Georgia; the Treaty of Indian Springs Folder, February 12, 1825; the Haiman Civil War Sword Factory in Columbus; the Gunboat Chattahoochee crew members; The Gallant City, the Civil War Centennial pageant; King's Gap in Harris County; Walker-Peters-Langdon House; Major Raphael J. Moses; extensive primary and secondary material on Brigadier General Paul J. Semmes, a Columbusite killed at Gettysburg; symposium papers from 1973 and 1974 conferences on pre-Columbian contacts held at Westville; and Westville correspondence and other records, 1968-1978.

The collection is divided into seven series:

Series 1 -- Subject Files Series 2 -- American Historic Preservation Commission Series 3 -- Westville Series 4 -- Institute for the Study of American Cultures (ISAC) Series 5 -- Lower Chattahoochee Area Planning and Development Committee Series 6 -- Research Notes Series 7 -- Artifacts