In late September 1805, the Corps of Discovery, led by Captains Meriwether Lewis and William Clark, struggled through the mountainous Idaho wilderness west of Lolo Pass. Finally, Clark forged ahead with a small band, hoping to find game (which they did, if you count one luckless wandering horse). On September 20, Clark’s party marched out of the forest onto “a leavel rich open Plain.” Their careful, friendly approach earned them a welcome into an Indian camp where, Clark said, “Those people treated us well”
As they moved on to another encampment, Clark noted “grt quantities of roots have been geathered and in heaps. Those roots are like onions, sweet when dried, and tolerably good in bread. I eate much & am Sick in the evening.”
Thus did the Expedition meet the Nez Perce for the first time, on Weippe Prairie a bit over 50 miles east of today’s Lewiston, Idaho. The onion-like roots were camas bulbs, a major staple of the Indian’s diet. Lewis and Clark were happy to trade with the natives for provisions, although the change in diet induced intestinal disorders for many of the Corps. including Lewis
Reference: Meriwether Lewis and William Clark, Gary E. Moulton (Ed.), The Definitive Journals of the Lewis and Clark Expedition, University of Nebraska Press, Lincoln (2002).