Replica source: Letter from Theodore Roosevelt to Quentin Roosevelt. Sagamore Hill National Historic Site. https://www.theodorerooseveltcenter.org/Research/Digital-Library/Record?libID=o275939. Theodore Roosevelt Digital Library. Dickinson State University.

Letter from Theodore Roosevelt to John Muir. Theodore Roosevelt Papers. Library of Congress Manuscript Division. https://www.theodorerooseveltcenter.org/Research/Digital-Library/Record?libID=o184892. Theodore Roosevelt Digital Library. Dickinson State University.

Notes on natural history. Theodore Roosevelt Birthplace National Historic Site. https://www.theodorerooseveltcenter.org/Research/Digital-Library/Record?libID=o284954. Theodore Roosevelt Digital Library. Dickinson State University.