Platte has become a highway for the fur traders.

For some days past, Captain Bonneville had been made sensible of the
great elevation of country into which he was gradually ascending by the
effect of the dryness and rarefaction of the atmosphere upon his wagons.
The wood-work shrunk; the paint boxes of the wheels were continually
working out, and it was necessary to support the spokes by stout props
to prevent their falling asunder. The travellers were now entering one
of those great steppes of the Far West, where the prevalent aridity
of the atmosphere renders the country unfit for cultivation. In these
regions there is a fresh sweet growth of grass in the spring, but it is
scanty and short, and parches up in the course of the summer, so that
there is none for the hunters to set fire to in the autumn. It is a
common observation that "above the forks of the Platte the grass does
not burn." All attempts at agriculture and gardening in the neighborhood
of Fort William have been attended with very little success. The grain
and vegetables raised there have been scanty in quantity and poor in
quality. The great elevation of these plains, and the dryness of the
atmosphere, will tend to retain these immense regions in a state of
pristine wildness.

In the course of a day or two more, the travellers entered that wild and
broken tract of the Crow country called the Black Hills, and here their
journey became toilsome in the extreme. Rugged steeps and deep ravines
incessantly obstructed their progress, so that a great part of the
day was spent in the painful toil of digging through banks, filling up
ravines, forcing the wagons up the most forbidding ascents, or swinging
them with ropes down the face of dangerous precipices. The shoes of
their horses were worn out, and their feet injured by the rugged and
stony roads. The travellers were annoyed also by frequent but brief