Jacques Marquette (1637-1675), a French Jesuit Father, and French-Canadian explorer Louis Jolliet (1645 - 1700) explored the Mississippi river as far south as the mouth of the Arkansas River in 1673. They were the first colonialists to map the northern portion of the Mississippi River.
Editors. "Francais Jacques Marquette explores the Mississippi". The Literary Encyclopedia. First published 20 December 2011
[http://www.litencyc.com/php/stopics.php?rec=true&UID=2627, accessed 23 September 2014.]