a. correspondence to Victor J. Evans regarding a Hunkpapa Sioux calendar, 1928-1929.
b. correspondence from D. F. MacCarthy regarding a comparison of the Sioux and Crow Indians, 1932.
c. correspondence to Angus McDonald regarding the Sioux attack on the Flathead camp on the Musselshell River in 1872, 1932.
d. correspondence from the National Park Service regarding Wind Cave, 1937.
e. correspondence from Campbell to Life regarding the Sioux belief that cranes are dangerous to children, 1943.
f. correspondence to and from Westerners Brand Book regarding Sioux burials and rites, 1947.
g. correspondence Holiday Magazine regarding mistakes made by another author about the Sioux, including a Sioux written language, Red Cloud, Sitting Bull, and Crazy Horse, 1948.