The collection consists principally of the typescript (with corrections in hand) of Horner's work, Wallowa River and Valley, dealing with regional history, as well as the Nez Percé Tribe. Other papers include correspondence (ca. 1889-1985); legal documents (1898-1931); patents for window construction (1921-1922); and manuscript materials (undated). Horner's main correspondent is Otis Halfmoon, a Catholic Nez Percé who assisted with the author's manuscript. The collection also includes a list of other contributors that assisted Horner in his research.