mountain ranges, hundreds of miles wide in places, split the continent? As they passed the future site of Fort Union, that realization was still four months away for Lewis and Clark.
The Indians inform that the yellowstone river is navigable for perogues and canoes nearly to its source in the Rocky Mountains, and that in it's course near these mountains it passes within less than half a day's march to a navigable part of the Missouri. it's extreem sources are adjacent to those of the Missouri, river platte, and I think probably with some of the South branch of the Columbia river. — Meriwether Lewis, April 26, 1805