St. Louis became Catlin’s base of operations for five trips he took between 1830 and 1836, eventually visiting fifty tribes. Two years later he ascended the Missouri River more than 3000 km to Fort Union Trading Post, near what is now the North Dakota-Montana border, where he spent several weeks among indigenous people who were still relatively untouched by European civilization. He visited eighteen tribes, including the Pawnee, Omaha, and Ponca in the south and the Mandan, Hidatsa, Cheyenne, Crow, Assiniboine, and Blackfeet to the north.