Letters, diary transcripts and research notes pertaining to the 1869 Cook-Folsom expedition into Yellowstone National Park were gathered or created by Chesnut during his employment at Bozeman Montana (1904-1907) and Washington, D.C. (1921-1922). In 1904, Chesnut met Charles W. Cook, an elderly farmer living in White Sulphur Springs, Montana. Cook, along with David E. Folsom and William Peterson, had explored the Yellowstone National Park region in 1869 and recorded their journey in a joint "diary" which had appeared in edited form several times during the intervening years. Cook gave Chesnut his original manuscript version of the diary from which Chesnut prepared a typed transcript. The typed transcript was then submitted by Chesnut to David E. Folsom of Diamond City, Montana, for his correction. In 1921, Chesnut was contacted by Oscar Mueller, a Lewistown, Montana attorney and son-in-law of Charles Cook requesting the return of the original manuscript version. Chesnut no longer had the original but provided a copy of the transcript then in his possession. The Chesnut papers include the 1904 transcript of the Cook-Folsom expedition diary prepared by Chesnut and corrected by David E. Folsom; letters written in 1921 and 1922 from Oscar Mueller, Horace Albright, and Stephen Mather all pertaining to the diary or to a planned appearance of Charles Cook at a celebration at Yellowstone National Park; a copy of the 1894 publication of the expedition diary as edited by Nathaniel Langford and corrected by David E. Folsom; miscellaneous research notes.