Photo: Missouri River by Ponca State Park, courtesy Nebraska Game and Parks Commission.
Charting the tributaries of the Missouri was a principal objective of the expedition.
July 30, 1804. Clark: the most butifull prospect of the River up & Down and the Countrey Opsd. prosented it Self which I ever beheld; The River meandering the open and butifull Plains, interspursed with Groves of timber, and each point Covered with Tall timber, Such as Willow Cotton sum Mullberry, Elm, Sucamore Lynn [linden] & ash (the Groves contain Hickory, Walnut, coffee nut & Oake in addition)
More from the journals about the Missouri River
August 24, 1804. Clark: In a northerly derection from the Mouth of this Creek in an emence Plain a hight Hill is Situated [Spirit Mound near Vermillion, South Dakota], and appears of a Conic form, and by the different nations of Indians in this quarter is Suppose to be the residence of Deavels. that they are in human form with remarkable large heads, and about 18 Inches high, that they are very watchfull and are arm'd with Sharp arrows with which they Can kill at a great distance; they are Said to kill all persons who are So hardy as to attempt to approach the hill; they State that tradition informs them that many Indians have Suffered by these little people, and among others three Mahar Men fell a sacrefise to their murceless fury not many Years Sence. So Much do the Maha, Soues, Ottoes and other neighbouring nations believe this fable, that no Consideration is Suffecient to induce them to approach the hill.
July 30, 1804. Clark: the most butifull prospect of the River up & Down and the Countrey Opsd. prosented it Self which I ever beheld; The River meandering the open and butifull Plains, interspursed with Groves of timber, and each point Covered with Tall timber, Such as Willow Cotton sum Mullberry, Elm, Sucamore Lynn [linden] & ash (the Groves contain Hickory, Walnut, coffee nut & Oake in addition)