MLA
Evans, Clement A. Letter from Clement A. Evans to General William E. Mickle (Atlanta, Georgia) - February 2, 1906. 1906. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 8, Folder 23. https://digital.library.emory.edu/purl/112m63xt7h-cor.
APA, 6th edition
Evans, C. A. (1906). Letter from Clement A. Evans to General William E. Mickle (Atlanta, Georgia) - February 2, 1906 (Box 8, Folder 23) [Correspondence]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/112m63xt7h-cor.
Chicago
Evans, Clement A. “Letter from Clement A. Evans to General William E. Mickle (Atlanta, Georgia) - February 2, 1906.” Correspondence. Civil War Collection, 1906. Box 8, Folder 23. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/112m63xt7h-cor.