Lewis and Clark's journey

In my opinion, the hardest part of Lewis and Clark's journey was the crossing of the Bitterroot Mountains. On the National Geographic website it states that they were so low on food at this point in the journey that they had to eat three of their horses. It also states that they would likely have died without the fresh horses that they received from Indians. Additionally the Lewis and Clark historic trail site states that they nearly starved when they crossed the mountains. Lewis-Clark.org states that in Lewis's Journal he says the snow was 12 to 15 feet, and that it invelloped them.  

Bitterroot Mountains Picture via Wikipedia