The Humason papers have been arranged, with only minor changes, according to the manner in which they had been found in the attic of the Carnegie Observatories. The correspondence covers the years 1930-1952. It contains both incoming and carbons of outgoing correspondence. The collections also includes a few press releases, newsletters, one manuscript in German, some ephemera, several black-and-white photographs and two black-and-white slides. Notable participants include: Ansel Adams, Robert Aitken, Loyal Aldrich, Lawrence Aller, C. T. Elvey, G. F. Fassett, George Gamow, Cecilia Gaposchkin, Warren K. Green, John C. Hogg, Edwin Powell Hubble, Wilhelminia Iwanowska, Martin Johnson, H. Spencer Jones, Egbert A. Kreiken, Wasley Krogdahl, Oliver Justin Lee, J. H. Moore, Thornton Page, Upton Sinclair, William T. Skilling, Harold C. Urey, H. L. Vanderlinden, Edwin Wald, Fletcher G. Watson, Frederick Weiss, Astronomy charted, Boston Museum of Science, California Institute of Technology, Carnegie Institution of Washington, Drake University, Grolier Society, Harvard College Observatory, Jet Propulsion Laboratory, Los Angeles Astronomical Society, Physics today, Popular astronomy, Popular mechanics, Science illustrated, and Scientific American (this is only a partial list).