Mexico might be reached by this route.

In the year of La Harpe's first exploration, one Du Tisne went up the
Missouri to a point six leagues above Grand River, where stood the
village of the Missouris. He wished to go farther, but they would not
let him. He then returned to the Illinois, whence he set out on
horseback with a few followers across what is now the State of Missouri,
till he reached the village of the Osages, which stood on a hill high up
the river Osage. At first he was well received; but when they found him
disposed to push on to a town of their enemies, the Pawnees, forty
leagues distant, they angrily refused to let him go. His firmness and
hardihood prevailed, and at last they gave him leave. A ride of a few
days over rich prairies brought him to the Pawnees, who, coming as he
did from the hated Osages, took him for an enemy and threatened to kill
him. Twice they raised the tomahawk over his head; but when the intrepid
traveller dared them to strike, they began to treat him as a friend.
When, however, he told them that he meant to go fifteen days' journey
farther, to the Padoucas, or Comanches, their deadly enemies, they
fiercely forbade him; and after planting a French flag in their
village, he returned as he had come, guiding his way by compass, and
reaching the Illinois in November, after extreme hardships.[375]

Early in 1721 two hundred mounted Spaniards, followed by a large body of
Comanche warriors, came from New Mexico to attack the French at the
Illinois, but were met and routed on the Missouri by tribes of that
region.[376] In the next year, Bienville was told that they meant to
return, punish those who had defeated them, and establish a post on the
river Kansas; whereupon he ordered Boisbriant, commandant at the
Illinois, to anticipate them by sending troops to build a French fort at
or near the same place. But the West India Company had already sent one
Bourgmont on a similar errand, the object being to trade with the
Spaniards in time of peace, and stop their incursions in time of
war.[377] It was hoped also that, in the interest of trade, peace might
be made between the Comanches and the tribes of the Missouri.[378]

Bourgmont was a man of some education, and well acquainted with these
tribes, among whom he had traded for years. In pursuance of his orders
he built a fort, which he named Fort Orleans, and which stood on the
Missouri not far above the mouth of Grand River. Having thus
acc