To the Senate of the United States:
When the convention of the 7th of January, 1806, was entered into with the Cherokees for the purchase of certain lands, it was believed by both parties that the eastern limit, when run in the direction therein prescribed, would have included all the waters of Elk River. On proceeding to run that line, however, it was found to omit a considerable extent of those waters, on which were already settled about 200 families. The Cherokees readily consented, for a moderate compensation, that the line should be so run as to include all the waters of that river. Our commissioners accordingly entered into an explanatory convention for that purpose, which I now lay before the Senate for consideration whether they will advise and consent to its ratification. A letter from one of the commissioners, now also inclosed, will more fully explain the circumstances which led to it.
Lieutenant Pike on his journey up the Mississippi in 1805-6, being at the village of the Sioux, between the rivers St. Croix and St. Peters, conceived that the position was favorable for a military and commercial post for the United States whenever it should be thought expedient to advance in that quarter. He therefore proposed to the chiefs a cession of lands for that purpose. Their desire of entering into connection with the United States and of getting a trading house established there induced a ready consent to the proposition, and they made, by articles of agreement now inclosed, a voluntary donation to the United States of two portions of land, the one of 9 miles square at the mouth of the St. Croix, the other from below the mouth of St. Peters up the Mississippi to St. Anthonys Falls, extending 9 miles in width on each side of the Mississippi. These portions of land are designated on the map now inclosed. Lieutenant Pike on his part made presents to the Indians to some amount. This convention, though dated the 23d of September, 1805, is but lately received, and although we have no immediate view of establishing a trading post at that place, I submit it to the Senate for the sanction of their advice and consent to its ratification, in order to give to our title a full validity on the part of the United States, when ever it may be wanting, for the special purpose which constituted in the mind of the donors the sole consideration and inducement to the cession.
Thomas Jefferson, Special Message Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/203617