Undaunted Courage: Meriwether Lewis, Thomas Jefferson, and the Opening of the American West

by Stephen E. Ambrose

That evening, Lewis described in his journal a phenomenon of the region, a repeated noise coming from the northwest at irregular intervals that resembled “precisely the discharge of a piece of ordinance of 6 pounds at the distance of three miles.” The men had often mentioned the sound to him, but Lewis had been sure they had been hearing thunder, until “at length walking in the plains the other day I heard this noise very distictly, it was perfectly calm clear and not a cloud to be seen.” He stopped and for an hour listened intently: he heard it twice more. “I have no doubt but if I had leasure I could find from whence it issued,” he wrote. He would hear it again on July 11 and then recalled that the Hidatsas had mentioned such a noise. Clark also heard it; like Lewis, he was certain there was a rational explanation, although none came to mind. No one since has explained it, but if Lewis and Clark said they heard it, it was there.II