Thereafter, he became a tireless advocate for opening Oklahoma to non-Indian settlement. An original '89er, Clarke served as president of the infant Oklahoma City Council and was acting mayor during the first year of the city's existence. Sidney Clarke died in Oklahoma City on June 18, 1909. The Clarke Collection documents all aspects of the man's life and career. Approximately one-third consists of holographic correspondence from the late nineteenth century.
Typescripts accompany many of the letters.
The collection is strong in constituent and newspaper reaction to national and local events, treaties with Indians and their subsequent removal from Kansas after the Civil War, the development of former Indian lands in Kansas by railroads and settlers, and the early history of Oklahoma. This series contains 0.79 cubic feet of correspondence, legislation, reports, clippings, military papers, and publications by Sidney Clarke and by others. The arrangement is chronological by year, and within the year by subject. Included are materials on Clarke's life in Massachusetts, his move to Kansas in 1859, and his military service during the Civil War. Prominent correspondents include James H. Lane, W. W. H. Lawrence, J. G. Blunt, and J. J. Ingalls.