This collection contains field notes written by Butler during the 1925 field season (April 11-August 20) of the Third Asiatic Expedition. It also contains a typed diary detailing his experiences in Mongolia and discussing expedition staff members. Correspondences include letters to and from Butler and his wife in Tianjin (Tientsin), China, and official correspondences. Also included are various lectures ("Speech to the Algonquin Club. Boston, Dec. 7, 1926"; "Expedition lecture with lantern slides, Tientsin, China, October, 1925"; "Notes for interpreter on Mongolian lecture to be delivered to the Japanese officers, April 5, 1926") and article drafts (The China Pony and Mapping with Third Asiatic Expedition) written by Butler, issues of periodicals (The Cavalry Journal, Vol. 35, July and October 1926; and The Military Engineer, Vol. 18, July/August 1926) containing the published articles and a letter in response, a formal report of the expedition written by Butler for Army officials, and newspaper clippings reporting on the expedition (primarily from The Los Angeles Times and The San Francisco Chronicle). There is also a felt patch with the expedition insignia and a box containing 38 bits of Mongolian flints. This collection provides insight into Butler’s cartography work on the Third Asiatic Expedition and his personal experiences in Mongolia and with other members of the expedition.