The majority of the papers are correspondence from Bullock and his wife, Katie, and to his mother, Mrs. C. A. Bullock of Hadley, Michigan. The letters contain details of missionary work, life in South America, political and social affairs in Chile and Argentina, and personal matters. Also covered in Bullock's letters is his work and interest in natural history, especially wildlife. An account of a trip Bullock took to Isla Dela Mocha in 1932 is included in the correspondence which discusses birds and insects.

Also included are weekly reports Bullock made while Agricultural Commissioner in Argentina, reports of church conferences, newspaper clippings on Bullock's activities from 1912 to 1921, and a 1902 commencement program from Michigan Agricultural College (now Michigan State University).