Long used by Native Americans, it became a thoroughfare between the Great Lakes and the Mississippi Valley for explorers, missionaries, and fur traders. Travelers from the east exited Lake Superior near Fond du Lac ("end of the lake", or more idiomatically "head of the lake", where Duluth is now located), and ascended the steep, rocky, and difficult gorge of the lower Saint Louis River, which falls some from the location of Carlton, Minnesota, through what is now Jay Cooke State Park to its outlet at the lake. Above Carlton travelers proceeded upstream through quieter stretches to the location of Floodwood, Minnesota, where they turned southwest up the sluggish East Savanna River in the bed of Glacial Lake Upham. Coming to a small rise, the travelers commenced the portage, which in its eastern reaches was marshy, mosquito-infested, and among the most unpleasant and even tortuous of all the routes taken by the voyageurs. Struggling waist-deep through the morass of the "boundless swamp", travelers eventually reached a hardwood forest, through which the trail ran to the West Savanna River, which drains to Big Sandy Lake and the Upper Mississippi River. In times of low water, the portage was drier but the river became too shallow for canoes, so voyageurs would continue to hike overland to the northeast bay of Big Sandy Lake.