In Volume II, Martin Plamondon presents a cartographic reconstruction of the Corps of Discovery's trek across the northwestern United States in 1805-06. Beginning a short distance above Fort Mandan, 190 maps depict the explorers' route on the Missouri River in North Dakota and Montana, over the continental divide to Idaho, and down westward-flowing waters to the Snake-Columbia confluence in central Washington.The maps contrast modern riverbeds to their courses at the time of the exploration. Also included are pertinent excerpts from the journals and depictions of significant geographical features. Plamondon has utilized the actual traverse measurements and notes recorded by William Clark for each day that the expedition was on the move.

This is the second of a three-volume set published by the WSU Press delineating the Corps' entire journey, both outbound and return, in 1804-06. Volume I, published in September 2000, includes 153 full-page maps of the explorers' route on the Missouri River from Illinois to North Dakota.