What bend of the Missouri River between Vermillion and Yankton, SD is named after a famed 19th century naturalist who stayed at Fort Vermillion in 1843? He was traveling on the Missouri River while researching his book on quadrupeds? Archives and Special Collections has his quadruped and bird books in the Chilson Collection.
Image from quadruped book in the Chilson Collection.
The answer and the source of this information can be found in Herbert Schell’s History of Clay County, 1976, page 13.