The Gilbert Gaines Collection comprises the personal papers and photographs of geologist Gilbert Gaines. The bulk of the collection consists of Gaines's photographs in two photo albums containing mostly 3x5 inch or smaller prints and approximately 1,430 35mm color slides. Included are many images of San Diego and southern California documenting Gaines's personal life and travels from the 1940s to 2002. Several images document Gaines's camping trips in the Cuyamaca Mountains and San Diego County Backcountry in the 1940s, and trips to Yosemite Valley in the 1950s. Gaines's trip to Thule Air Base in Greenland and the surrounding glaciers is well documented by a large series of 35mm slides. Also included are images from Gaines's travels to the east coast, most notably Fort Eustis, Virginia, as well as Washington D.C. and New York.

The collection is divided into two series: Personal Papers, and Photographs. The Personal Papers series includes military, academic and professional records, as well as a small amount of correspondence. There is also a framed collage of printed ephemera produced by Acorn Press, a San Diego printing company connected to Gaines's relative Sydney Goldstein. The Photographs series includes mostly 35mm film slides, two photo albums, and a few photographic prints.