The collection documents Gillingham's career as a geological consultant. The collection is arranged into six series: W.R. Grace & Co.; Uranium Mining; Phosphate Mining; Reports; Education; and Reference cards.

The W.R. Grace & Co series includes meeting minutes of the Grace mining division, profit plan summaries, memorandums, and company correspondence. Gillingham's work for Grace involved the pursuit of a mining contract in Turkey, zinc mining in Gainesboro, Tennessee, coal mining in West Virginia and California, Gold mining in California, and a copper-nickel project in Minnesota. Gillingham's work with W.R. Grace in Turkey documents the firm's difficulty negotiating mining rights with the government, and the records include monthly reports, and correspondence with W.R. Grace's agents in Turkey and the United States Tariff Commission. Grace's zinc, coal, gold, and copper-nickel records consist of monthly reports, drilling logs, and correspondence.

The uranium mining series documents Gillingham's work as a geologist for the Atomic Energy Commission (AEC). The AEC records include reports about uranium supply and a collection of Look magazine articles about "Atoms for Peace" and constructive uses of nuclear explosions. Gillingham's files contain information about a contract agreement between United Nuclear Corp (UNC), and Indiana & Michigan Electric Company and the American Electric Power Service Company (AEP). In 1967, AEP contracted UNC to provide fuel for a nuclear reactor that was to be built in Michigan. The original contract was breached by AEP after construction delays forced the company to delay the uranium delivery dates. UNC filed a lawsuit against AEP to force compliance with the original contract. The contract, as well as the court filings, is included in the collection.

The phosphate mining series includes reports on the phosphate mining companies Gillingham worked for, the geology of phosphate deposits, and other notes on phosphate mining.

The reports, 1936-1980, include information on various mining subjects, such as geophysical exploration for minerals, other possible mining projects, mining prospects in the United States as well as in other countries, and new exploration methods. Also included is a report written by Gillingham for the Navy on the operations during the Battle of Leyte Gulf in 1944.

Gillingham's papers from graduate level geology courses constitute Series V. It also included materials used by Gillingham to practice Spanish, French, and German.

Gillingham compiled an extensive collection of reference cards. Many of the cards are a bibliography of relevant mining and geological publications; others include information on specific projects. One large section of cards is labeled "capital costs" and refers to mining expenses from projects across the globe from 1956 through 1974.