Four months into their journey up the Missouri River, the Lewis & Clark party found themselves at the mouth of the White River, in southern South Dakota. From there, the Missouri would lead them NNW to Fort Mandan, their wintering site in west-central North Dakota.
This stretch of their journey was disrupted by a standoff with the Teton Sioux, a tribe that ruled the Missouri Valley near present-day Pierre; fortunately, the confrontation was settled without conflict. Otherwise, this section of the Missouri was notable for its numerous sandbars and braided channels, forded by large herds of bison. French traders, having descended along the Cheyenne River from the Black Hills, reported numerous goats (pronghorns), "white bears" (grizzlies) and curved-horn mountain sheep (bighorn sheep) in that mountainous region. The Lewis and Clark party came across their first evidence of grizzlies near the mouth of the Moreau River in northern South Dakota, and eventually encountered one south of present-day Bismarck, North Dakota; bison, wolves, elk, deer (including mule deer) and beaver were all reported to be abundant along this stretch of the Missouri.
By late October, 1804, periods of snow swept across the Northern Plains and the travelers settled in amidst the Mandan Tribe, establishing Fort Mandan near the mouth of the Knife River. Constructing their winter shelters through November, as flocks of migrant geese passed overhead, they completed them just in time; by late November and into December, overnight temperatures fell as low as 40 degrees below zero (F), more than a foot of snow covered the ground and frostbite had become a frequent problem. Grounded for five months, they had covered 1600 river miles since leaving St. Louis.