Occasionally in the media we all hear reports of someone discovering a lost copy of a founding document at a flea market, an unknown manuscript of a famous author at an estate sale, or a priceless painting set out with the garbage. Movies like National Treasure heighten our interest in the possible existence of such undiscovered treasures. So while browsing shelves of tattered volumes at a used bookstore or thrift shop, who can help but let their imagination run a little wild?
The Kansas Historical Society has made a few chance discoveries of its own. A particularly interesting one dates back to 1886. One day, John Speer, a director of the Historical Society, passed a used bookshop in Lawrence, Kansas, and saw a stack of large, old books piled up on the sidewalk. Looking over the volumes, he immediately recognized their importance: they were the ledger books of William Clark (of Lewis and Clark, “Voyage of Discovery,” fame) while Clark was Superintendent of Indian Affairs at St. Louis, Missouri (1810s-1830s).
Without speaking to the shopkeeper, Speer caught the first train to Topeka to see Judge Franklin G. Adams, secretary of the Historical Society, and tell him of the discovery.
Adams and Speer took the next train back to Lawrence. At the bookstore, Adams casually reviewed the volumes. He then approached the bookseller and, in an indifferent way, inquired about the price. The bookseller indicated he was planning to sell the books to the paper mill and thought he should get at least as much as the mill would give him. The two settled on a price of $33.00 (about one dollar per volume). Adams and Speer packed up the books and shipped them to Topeka to be added to the Historical Society’s collections.
The twenty-nine bound folio volumes discovered that day include the records of William Clark and other Superintendents of Indian Affairs, including field notes and plats of Indian lands, 1830-1836; treaties and other agreements between the U.S. and various tribes, 1831-1838; and other records of the Missouri (1807-1821), Central (1822-1851), and St. Louis (1851-1855) Superintendencies of Indian Affairs. The collection also includes records of the Missouri Fur Co., 1812-1817, of which Clark served as a director. See William Clark for more selections from these volumes in Kansas Memory. For a more detailed description of the collection see the William Clark Papers. 
How the books came to be at the Lawrence bookstore is still a mystery. After Clark’s death in 1838, the St. Louis office relocated several times before settling in Lawrence, Kansas, in 1869. When the office finally closed in 1878, General John Henry Hammond was assigned to inventory the papers and send them to Washington, D.C. Were the books purchased earlier in St. Louis as some sources suggest? Or did they follow the office to Lawrence in 1869 but fail to be shipped to Washington, D.C. in 1878?
Sources:
William Connelly, “Indian Office Manuscripts,” August 26, 1929
Kansas City Times, “Kansas Owns a Missouri Historical Treasure,” March 17, 1947
Transactions of the Kansas State Historical Society, v3 (1886) 49-51
Ernest Staples Osgood, ed., “Introduction,” The Field Notes of Captain William Clark, 1803-1805 (New Haven, Yale University Press, 1964) xxxii-xxxv