NY, Viking, (1962). Matthiessen's own copy of his third book of nonfiction, recounting the Harvard-Peabody Expedition to New Guinea. Laid in are two news clippings about New Guinea tribes, and a letter from (apparently) the director Robert M. Young regarding The Ballad of Gregorio Cortez and Alambrista! and including a copy of a 1966 letter from Cornelio van Kessel in Manila, 4 pages, densely spaced, recounting his version of the 1961 disappearance and death of Michael Rockefeller. Matthiessen's retained copy of his reply to Young is also included. The young Rockefeller's disappearance on the trip was a great mystery, and the competing theories had him either drowning or being killed and eaten by the local tribesmen. Van Kessel's 1966 letter affirms most of what came out in a 2015 book on the subject that is considered the most conclusive analysis. Offsetting to the pages where the clippings were laid in. Very good in a very good, edgeworn dust jacket, heavily worn at the folds. Together with: Matthiessen's copies of three books by Karl Heider, covering the Harvard-Peabody Expedition and the Dani tribe: first, Gardens of War (with Robert Gardner) [NY: Random House, 1968]: "In the beginning we numbered five: Jan, Michael Rockefeller, Karl Heider, Peter Matthiessen, and myself [Gardner]..." Signed by the authors as "Bob" and "Karl", with the additional notation "Cambridge Man '69." Near fine in a very good, price-clipped dust jacket. Second, The Dugum Dani [Chicago: Aldine, 1970]. Inscribed by Heider to Matthiessen (near fine in a very good dust jacket); and, third, a near fine copy in wrappers of Grand Valley Dani, third edition, [Harcourt Brace, 1997], also inscribed by Heider to Matthiessen,, "who was in it at the beginning." Matthiessen makes several appearances in the text of the latter two books, and has some of the photo credits on Gardens of War. Lastly, also included is Matthiessen's copy of the uncorrected proof of Milt Machlin's The Search for Michael Rockefeller [NY: Putnam's, 1972], which lists Under the Mountain Wall in the bibliography. Spine slanted and stained, about very good in tall wrappers. A more definitive group of books and related materials on the subject of this expedition would be hard, if not impossible, to assemble. [#032379] SOLD