Some years after his purported journey from the Atlantic to the Pacific, Moncacht-Apé related his adventures and itinerary to Antoine-Simon Le Page du Pratz, a French explorer and ethnographer in the colony of Louisiana.
For most of his time in La Louisiane, where he remained until 1734, Le Page lived at a trading post at Natchez, Mississippi, explored the local territory, and observed its Native peoples.
[1] In his memoir, published in Paris in installments beginning in 1753, Le Page describes his attempts to uncover the history of tribes in Louisiana that, unlike the Natchez, believed that they came from far away in the northwest.
In it, Le Page published a map based on Moncacht-Apé's itinerary; it became well-known and was compared by Denis Diderot in his Encyclopédie to charts prepared by other explorers.
Moncacht-Apé's failure to mention crossing the Rocky Mountains may have inspired their overly optimistic belief that they could easily carry a boat from the headwaters of the Missouri to the westward-flowing Columbia River.
[4] A second account of Moncacht-Apé's transcontinental journey was given by Jean-François-Benjamin Dumont de Montigny, a French army officer, in Chapter 41 of his Memoirs historiques sur la Louisiane (wherein the Indian's name is given as "Moncachtabé").
Some historians speculate that Le Page embellished Moncacht-Apé's journey with details supplied by fur traders and Indians who had traveled into the interior of the continent, then mostly unknown to Europeans.