Clark drew this map of the falls of the Missouri, including the expedition's portage-route around them, during the third week in June, 1805. It is in the codex, or manuscript book, known as Voorhis No. 1, which contains Clark's daily journals for the period April 7 through July 3, 1805. Voorhis No. 1 is one of three red-bound journals of Clark's that Reuben Thwaites found at the New York home of Julia Clark Voorhis in 1903. Mrs. Voorhis had obtained them from the estate of her father, William Clark's fourth child, George Rogers Hancock Clark.2 The Voorhis Collection is now part of the Clark Family Collection in the William Clark Papers at the Missouri Historical Society Archives in St. Louis, Missouri.
The importance of this segment of the Missouri River in the history of the Lewis and Clark expedition is reflected in Clark's journal entry for July fourth, written at the upper portage camp: "I employ my Self drawing a Copy of the river to be left at this place for fear of Some accident in advance."
An engraving based on Clark's sketch was printed in Paul Allen's edition of Nicholas Biddle's paraphrase of the expedition's journals (1814).