The papers of Ephraim George Squier (1821-1888) span the years 1841-1888, with the bulk of the material concentrated in the period 1846-1874. The papers include correspondence, diplomatic and business records, lectures, articles, reference and bibliographic notes, drawings, and scrapbooks of clippings assembled by Squier. The collection, in English, Spanish, French, and German, is arranged in the following series: General Correspondence; Honduran Representatives File; Honduras Interoceanic Railway File; Speech, Article, and Book File; Miscellany; and Addition.

Squier's interest in archaeology, ethnology, and Central American affairs are documented in the General Correspondence. Also represented are Squier's writings, publishing interests, and membership in learned societies. A few items concern his connection with the publisher Frank Leslie, and there are no letters of his wife, Miriam Florence Folline (later Mrs. Frank Leslie), an editor, author, and feminist.

The Honduran Representatives File consists of correspondence of Don Luis Molina, 1857-1867, Honduran minister to the United States. and Squier's correspondence as the Honduran consul-general in New York, 1869-1873.

The Honduras Interoceanic Railway File contains a variety of papers dealing with the ill-fated Honduras Interoceanic Railway, Ltd., for which Squier was attorney and agent. The file includes correspondence, inventories, reports, construction plans, and employee lists. Among the correspondence are letters of John C. Trautwine, the project's chief engineer. A small handwritten volume titled "Barometrical & Therm. Obs.," dated 1853 and containing crude maps, tables, and drawings, is filed in the Miscellany series.

Archaeology and ethnology are the chief focus of the Speech, Article, and Book File, which contains reference notes, drafts of books, and articles and lectures by Squier. Represented are manuscripts of what appear to be articles and book chapters on Nicaragua and drafts of Ancient Monuments of the Mississippi Valley. In addition, there are reference and bibliographical notes dealing with Indians, Mexico, Central America, archaeology, languages, hieroglyphics, religion, history, government, and diplomatic affairs. Among the items are numerous drawings and diagrams of archaeological interest which show implements, architecture, and locations of sites, and a printed bibliography dated 1876 listing works by Squier.

The Miscellany houses papers related to two professional societies in which Squier held office, the American Ethnological Society and the Anthropological Society of New York, papers pertaining to Central America, a journal of Squier's travels in Central America in 1849-1850, two scrapbooks of printed material consisting mostly of articles by Squier and others, and miscellaneous fragments.

The Addition consists of a bound report dated 1858 from Squier to the directors of the Honduras Interoceanic Railway Company Limited, setting forth the results of his activities as director of the land survey for the feasibility of a rail linkage across Honduras between the Atlantic and Pacific oceans. The volume also contains reports of engineers working with Squier on the project. Also included are articles and maps relating to the survey.

Correspondents include Louis Agassiz, León Alvarado, Henry B. Anthony, John Russell Bartlett, Samuel Birch, E. H. Davis, Joseph Barnard Davis, George R. Gliddon, Joseph Henry, José de Marcoleta, Matthew Fontaine Maury, Brantz Mayer, Charles Eliot Norton, Josiah Clark Nott, Frederick Ward Putnam, Henry Shelton Sanford, Buckingham Smith, Henry Stevens, John C. Trautwine, William W. Turner, and Thomas Wright.