Lemhi Pass is where the expedition first crossed the Continental Divide.
August 12, 1805. Lewis: at the distance of 4 miles further the road took us to the most distant fountain of the waters of the Mighty Missouri in surch of which we have spent so many toilsome days and wristless nights. thus far I had accomplished one of those great objects on which my mind has been unalterably fixed for many years, judge then of the pleasure I felt in all[a]ying my thirst with this pure and ice-cold water which issues from the base of a low mountain or hill of a gentle ascent for 1/2 a mile.
Photo courtesy Ralph Maughan.