y August of 1805 Meriwether Lewis was desperate to find the Shoshone Indians. Lewis had long deemed the Shoshones and their horses essential for an expected portage across the continental divide. Once beyond this ridge Lewis expected to find the waters that would take the Expedition for Northwestern Discovery from the Missouri River drainage to their ultimate destination—the Pacific Ocean.

What Lewis could not have known is that coming to understand the complex geography of the Columbia River country would confound him and Clark for the next two months. But before proceeding west with Lewis to the Columbia, it may be best to first explicate the hazy understanding he and Clark had about this Great River of the West on verge of their first physical encounter with it. Phrased in a modern idiom: what did Lewis and Clark know about the Columbia, and when did they know it? (Nicandri:2005)