To learn more about Clarence King, one of the protagonists of Passing Strange, see:
Thurman Wilkins, Clarence King: A Biography, revised and enlarged edition (Albuquerques: University of New Mexico Press, 1988)
James Gregory Moore, King of the 40th Parallel: Discovery in the American West (Stanford: Stanford University Press, 2006)
Patricia O'Toole, The Five of Hearts: An Intimate Portrait of Henry Adams and His Friends, 1880-1918
Aaron Sachs, The Humboldt Current: Nineteenth-Century Exploration and the Roots of American Environmentalism (New York: Viking, 2006)
Robert Wilson, The Explorer King: Adventure, Science, and the Great Diamond Hoax — Clarence King in the Old West (New York: Scribner, 2006)
King's 1872 book, Mountaineering in the Sierra Nevada, remains in print in various editions, as does Henry Adams's The Education of Henry Adams which contains the author's admiring account of King. The best collection of first-hand accounts of King's character remains Clarence King Memoirs: The Helmet of Mambrino published by King's friends in 1904, shortly after his death.