BUCHANAN, James (1791-1868). Autograph letter signed ("James Buchanan"), as Secretary of State, to General Persifor F. Smith. Washington, D.C., 24 December 1848. 1 page, 4to, faint staining, minor nicking at upper and right edges at folds, short tear to center fold. Buchanan sends a letter of introduction to Persifor F. Smith, commander of the Pacific Division of the United States Army after the Mexican War. The introducee, Caleb Lyon, was appointed U.S. Consul at Shanghai by President Polk in 1847. In 1848, he resigned the post to go to California, where gold had just been discovered; there, he was chosen secretary of the state of California's Constitutional Convention of 1849.