It is to be remembered, of course, that trading of this sort to
Mexico was not altogether a new thing. Sutlers of the old fur
traders and trappers already had found the way to New Spain from
the valley of the Platte, south along the eastern edge of the
Rockies, through Wyoming and Colorado. By some such route as that
at least one trader, a French creole, agent of the firm of Bryant
& Morrison at Kaskaskia, had penetrated to the Spanish lands as
early as 1804, while Lewis and Clark were still absent in the
upper wilderness. Each year the great mountain rendezvous of the
trappers--now at Bent's Fort on the Arkansas, now at Horse Creek
in Wyoming, now on Green River in Utah, or even farther beyond
the mountains--demanded supplies of food and traps and ammunition
to enable the hunters to continue their work for another year.
Perhaps many of the pack-trains which regularly supplied this
shifting mountain market already had traded in the Spanish
country.

It is not necessary to go into further details regarding this
primitive commerce of the prairies. It yielded a certain profit;
it shaped the character of the men who carried it on. But what is
yet more important, it greatly influenced the country which lay
back of the border on the Missouri River. It called yet more men
from the eastern settlements to those portions which lay upon the
edge of the Great Plains. There crowded yet more thickly, up to
the line between the certain and the uncertain, the restless
westbound population of all the country.

If on the south the valley of the Arkansas led outward to New
Spain, yet other pathways made out from the Mississippi River