When Wilkinson's name was smirched by Burr's conspiracy the Lieutenant likewise fell under suspicion, for it was believed that his south-western trip was undertaken in pursuance of some of Wilkinson's schemes.

Unquestionably this trip was intended by Pike to throw light on the exact nature of the Spanish boundary claims.
In all probability he also intended to try to find out all he could of the military and civil situation in the northern provinces of Mexico.
Such information could be gathered but for one purpose; and it seems probable that Wilkinson had hinted to him that part of his plan which included an assault of some kind or other on Spanish rule in Mexico; but Pike was an ardent patriot, and there is not the slightest ground for any belief that Wilkinson dared to hint to him his own disloyalty to the Union.
He Ascends the Mississippi.
In August, 1805, Pike turned his face towards the head-waters of the Mississippi, his purpose being both to explore the sources of that river, and to show to the Indians, and to the British fur traders among them, that the United States was sovereign over the country in fact as well as in theory.

He started in a large keel boat, with twenty soldiers of the regular army.

The voyage up-stream was uneventful.

The party lived largely on game they shot, Pike himself doing rather more hunting than anyone else and evidently taking much pride in his exploits; though in his journal he modestly disclaimed any pretensions to special skill.
Unlike the later explorers, but like Lewis and Clark, Pike could not avail himself of the services of hunters having knowledge of the country.