Siouan languages
Siouan or Siouan–Catawban is a language family of North America that is located primarily in the Great Plains, Ohio and Mississippi valleys and southeastern North America with a few other languages in the east.
Mandan language
Mandan was initially thought to be closely related to Hidatsa and Crow. However, since Mandan has had language contact with Hidatsa and Crow for many years, the exact relationship between Mandan and other Siouan languages (including Hidatsa and Crow) has been obscured and is currently undetermined. Thus, Mandan is most often considered to be a separate branch of the Siouan family.