 Marquette and Jolliet were the first to map the northern portion of the Mississippi River.They confirmed that it was easy to travel from the St. Lawrence River through the Great Lakes all the way to the Gulf of Mexico by water, that the native peoples who lived along the route were generally friendly, and that the natural resources of the lands in between were extraordinary.New France officials led by LaSalle followed up and erected a 4,000-mile network of fur trading posts.