 Archaeological evidence , especially in Missouri , suggests that man first made his presence in the watershed of the Missouri River between 10 @,@ 000 and 12 @,@ 000 years ago at the end of the Pleistocene . During the end of the last glacial period , a great migration of humans began , traveling via the Bering land bridge from Eurasia into and throughout the Americas . As they traveled slowly over centuries , the Missouri River formed one of the main migration paths . Most settled in the Ohio Valley and the lower Mississippi River Valley , but many , including the <unk> builders , stayed along the Missouri , becoming the ancestors of the later indigenous peoples of the Great Plains . 
