Material in the public domain. No restrictions on use.
Curtis, Sam'l P. "The Army of the South-West, and the First Campaign in Arkansas. Chapter Fourth: Official History of the Battle of Pea Ridge—The Preliminary Report of General Curtis." The Annals of Iowa 1867 (1867), 771-781.
Available at: http://ir.uiowa.edu/annals-of-iowa/vol1867/iss1/4