MLA
Blake, G. M. Letter from G. M. Blake (Columbia, S.C.) to "Dear Mother." G. M. Blake Served with the 6th South Carolina Cavalry Regiment, Also Known as Aiken's Rangers or Dixie Rangers and Later Served in the Signal Corps - August 26, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 31. https://digital.library.emory.edu/purl/0752fqz6zf-cor.
APA, 6th edition
Blake, G. M. (1862). Letter from G. M. Blake (Columbia, S.C.) to "Dear Mother." G. M. Blake served with the 6th South Carolina Cavalry Regiment, also known as Aiken's Rangers or Dixie Rangers and later served in the Signal Corps - August 26, 1862 (Box 1, Folder 31) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/0752fqz6zf-cor.
Chicago
Blake, G. M. “Letter from G. M. Blake (Columbia, S.C.) to ‘Dear Mother." G. M. Blake Served with the 6th South Carolina Cavalry Regiment, Also Known as Aiken's Rangers or Dixie Rangers and Later Served in the Signal Corps - August 26, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 1, Folder 31. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/0752fqz6zf-cor.