The Snake River rises in the Yellowstone area and flows generally westward to become the Columbia’s largest tributary, joining the latter near the Tri-Cities in Washington state. West of Yellowstone it crosses Idaho through the Snake River plain. A west-flowing river sounds like it should have been a highway for the westbound emigrants, and to some degree it was. It was not an artery like the great rivers of the east, however. It is blocked by waterfalls in its upper reaches (of which the lowermost is Shoshone Falls). Even below…
