The La Salle Expedition on the Mississippi River: A Lost Manuscript of Nicolas de La Salle, 1682. The La Salle Expedition on the Mississippi River presents the definitive English translation of Nicolas de La Salle's diary account of Rene Robert Cavelier, Sieur de La Salle's 1682 discovery expedition of the Mississippi River from Canada to the Gulf of Mexico. This previously unknown manuscript copy of a diary by Nicolas La Salle (who was not related to the explorer) was discovered recently in the collection of rare books in the Texas State Archives. La Salle's successful journey down the Mississippi culminated in an internationally recognized French claim over the river and lands later called the Louisiana Territory, which the United States acquired by treaty from France two hundred years ago. La Salle's 1682 expedition and the subsequent Louisiana Purchase of 1803 shaped both the dimensions and character of this nation and provided a platform for westward expansion into Texas and beyond to the Pacific.