The expedition halted for the winter in later October. With the other men, York labored for days, cutting trees and building a small fort near the villages of two Indian tribes, the Mandan and the Hidatsa.
The Hidatsa chief wet his finger and rubbed at York's skin, expecting it to be paint and to wash away. Surprised that York's color did not wash off, the chief proclaimed him as "big medicine". York found himself honored by both the Mandan and Hidatsa tribes.
One December night, the temperature fell to 45 egrees below zero, causing the men to huddle in their shelters. When the air warmed to zero, they hunted for food. Clark, York, and fourteen others killed a deer and eight bison. York and several others returned to the fort with frostbitten feet.
By early April, the Missouri River was free of ice. The explorers prepared to continue on their journey. A dozen men broke apart from the main body and headed downstream in a keelboart. The boat contiained maps, written reports, animal skins, and other cargo for President Jefferson. York sent a gift of a robe made from bison skin to his wife in Kentucky.
The other explorers continued upriver in the two pirogues and six new canoes they had fashioned from tree trunks. The Corps of Discovery now had two new members: a teenage girl named Sacagawea and her month old son. Sacagawea spoke the Shoshone language, and Lewis and Clark hoped that she could help them trade with that tribe for horses, which they would need to cross the Rocky Mountains.