The passage to the Western Sea was a constant preoccupation for explorers, who believed in the existence of a gulf that opened into the Pacific Ocean. Written reports on the subject were received at Court regularly and in great number, and in 1720, the King sent Pierre-François-Xavier de Charlevoix to investigate. For a period of more than 20 years beginning in 1726, a family of Canadian explorers, the La Vérendryes, were dedicated to this single goal. For the expeditions that he had financed by merchants, Pierre Gaultier de La Vérendrye followed the information offered by the Aboriginal inhabitant named Ochaga. As he pushed on further, a number of fortified trading posts were built, from the shores of Lake La Pluie (Minnesota) to the Paskoya River (Saskatoon). La Vérendrye also attempted to pacify the Aboriginal nations encountered: Mandan, Prairie Cree, Assiniboine, Menominee and Fox. His sons pursued the quest to the foothills of the Rockies, near Pierre (North Dakota). It was discovered that high mountains stood between the plains and the ocean, and posed an obstacle. The English and French War brought an end to exploration, and the Western trading posts were abandoned.

The Western Sea
Carte copiée sur celle tracée par le sauvage Ochagach et autres [Map copied from the one drawn by the savage Ochagach and others], no date
FR CAOM COL E 199 dossier La Vérendrye