Missouri River above Great Falls, Gates of the Mountains — Patrick Gass: July 23, 1805

and at the same time Captain Clarke and four men went on
again to endeavour to meet with some of the natives. We had
rapid water, and passed a great number of islands. Capt.
Clarke and his men killed four deer and a cabre, and left the
skins and meat on the horse, where we could easily find them.
The course of the river all day was nearly from the south,
through a valley of 10 or 12 miles wide. The mountains are
not so high nor so rocky, as those we passed. Large timber
is not plenty, but there are a great quantity of small shrubs
and willows. We passed a small river on the south side, and
some banks of very white clay. We encamped on an island,
having made 24 miles.