MLA
Curtis, George C. Letter from George C. Curtis (Camp near [?]) to His Father Regarding Union General Ambrose Burnside's "Mud March" and the Soldiers' Opinion of Union Generals Ambrose Burnside, Joseph Hooker, and George B. McClellan. Curtis' Regiment, the Identify of Which Is Not given, Was with the Army of the Potomac near Fredericksburg in 1863 - January 26, 1863. 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 19, Folder 17. https://digital.library.emory.edu/purl/668x95x7gs-cor.
APA, 6th edition
Curtis, G. C. (1863). Letter from George C. Curtis (Camp near [?]) to his father regarding Union general Ambrose Burnside's "Mud March" and the soldiers' opinion of Union generals Ambrose Burnside, Joseph Hooker, and George B. McClellan. Curtis' regiment, the identify of which is not given, was with the Army of the Potomac near Fredericksburg in 1863 - January 26, 1863 (Box 19, Folder 17) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/668x95x7gs-cor.
Chicago
Curtis, George C. “Letter from George C. Curtis (Camp near [?]) to His Father Regarding Union General Ambrose Burnside's ‘Mud March’ and the Soldiers' Opinion of Union Generals Ambrose Burnside, Joseph Hooker, and George B. McClellan. Curtis' Regiment, the Identify of Which Is Not given, Was with the Army of the Potomac near Fredericksburg in 1863 - January 26, 1863.” Letters (correspondence). Civil War Collection, 1863. Box 19, Folder 17. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/668x95x7gs-cor.