While the Ohio country--the lower half of the States of Ohio, Indiana, and Illinois--was throwing off its frontier character, the remoter Northwest was still a wilderness frequented only by fur-traders and daring explorers. And that far Northwest by the sources of the Mississippi had been penetrated by few white men since the seventeenth century. The earliest white visitors to the upper Mississippi are not clearly known. They may have been Pierre Radisson and his brother-in-law, Ménard des Grosseilliers, who are alleged to have covered the long portage from Lake Superior to the Mississippi in or about 1665; but the matter rests entirely on how one interprets Radisson's vague account of their western perambulations. At all events, in 1680--seven years after the descent of the river from the Wisconsin to the Arkansas by Marquette and Joliet--Louis Hennepin, under instructions from La Salle, explored the stream from the mouth of the Illinois to the Falls of St. Anthony, where the city of Minneapolis now stands, five hundred miles from the true source. There the matter of exploration rested until the days of Thomas Jefferson, when the purchase of Louisiana lent fresh interest to northwestern geography. In 1805 General James Wilkinson, in military command in the West, dispatched Lieutenant Zebulon M. Pike with a party of twenty men from St. Louis to explore the headwaters of the great river, make peace with the Indians, and select sites for fortified posts. From his winter quarters near the Falls, Pike pushed northward over the snow and ice until, early in 1806, he reached Leech Lake, in Cass County, Minnesota, which he wrongly took to be the source of the Father of Waters. It is little wonder that, at a time when the river and lake surfaces were frozen over and the whole country heavily blanketed with snow, he should have found it difficult to disentangle the maze of streams and lakes which fill the low-lying region around the headwaters of the Mississippi, the Red River, and the Lake of the Woods. In 1820 General Cass, Governor of Michigan, which then had the Mississippi for its western boundary, led an expedition into the same region as far as Cass Lake, where the Indians told him that the true source lay some fifty miles to the northwest. It remained for the traveler and ethnologist Henry Schoolcraft, twelve years later, to discover Lake Itasca, in modern Clearwater County, which occupies a depression near the center of the rock-rimmed basin in which the river takes its rise.