MLA
Evans, Robert. Letter from Robert Evans (Gordonsville, Virginia) to His Wife, Sarah Evans. Evans Served in Company H of the 27th Georgia Infantry Regiment and Died during the Siege of Petersburg on June 15, 1864 - March 8, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 22. https://digital.library.emory.edu/purl/327mpg4g41-cor.
APA, 6th edition
Evans, R. (1862). Letter from Robert Evans (Gordonsville, Virginia) to his wife, Sarah Evans. Evans served in Company H of the 27th Georgia Infantry Regiment and died during the Siege of Petersburg on June 15, 1864 - March 8, 1862 (Box 3, Folder 22) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/327mpg4g41-cor.
Chicago
Evans, Robert. “Letter from Robert Evans (Gordonsville, Virginia) to His Wife, Sarah Evans. Evans Served in Company H of the 27th Georgia Infantry Regiment and Died during the Siege of Petersburg on June 15, 1864 - March 8, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 3, Folder 22. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/327mpg4g41-cor.