To the Senate and House of Representatives of the United States:
In pursuance of a measure proposed to Congress by a message of January 18, 1803, and sanctioned by their approbation for carrying it into execution, Captain Meriwether Lewis, of the First Regiment of infantry, was appointed, with a party of men, to explore the river Missouri from its mouth to its source, and, crossing the highlands by the shortest portage, to seek the best water communication thence to the Pacific Ocean; and Lieutenant Clarke was appointed second in command. They were to enter into conference with the Indian nations on their route with a view to the establishment of commerce with them. They entered the Missouri May 14, 1804, and on the 1st of November took up their winter quarters near the Mandan towns, 1,609 miles above the mouth of the river, in latitude 47° 21' 47" north and longitude 99° 24' 45" west from Greenwich. On the 8th of April, 1805, they proceeded up the river in pursuance of the objects prescribed to them. A letter of the preceding day, April 7th, from Captain Lewis is herewith communicated. During his stay among the Mandans he had been able to lay down the Missouri according to courses and distances taken on his passage up it, corrected by frequent observations of longitude and latitude, and to add to the actual survey of this portion of the river a general map of the country between the Mississippi and Pacific from the thirty-fourth to the fifty-fourth degree of latitude. These additions are from information collected from Indians with whom he had opportunities of communicating during his journey and residence with them. Copies of this map are now presented to both Houses of Congress. With these I communicate also a statistical view, procured and forwarded by him, of the Indian nations inhabiting the Territory of Louisiana and the countries adjacent to its northern and western borders, of their commerce, and of other interesting circumstances respecting them.
In order to render the statement as complete as may be of the Indians inhabiting the country west of the Mississippi, I add Dr. Sibley's account of those residing in and adjacent to the Territory of Orleans.
I communicate also, from the same person, an account of the Red River, according to the best information he had been able to collect.
Having been disappointed, after considerable preparation, in the purpose of sending an exploring party up that river in the summer of 1804, it was thought best to employ the autumn of that year in procuring a knowledge of an interesting branch of the river called the Washita.
This was undertaken under the direction of Mr. Dunbar, of Natchez, a citizen of distinguished science, who had aided and continues to aid us with his disinterested and valuable services in the prosecution of these enterprises. He ascended the river to the remarkable hot springs near it, in latitude 34° 31' 4.16", longitude 92° 50' 45" west from Greenwich, taking its courses and distances, and correcting them by frequent celestial observations. Extracts from his observations and copies of his map of the river from its mouth to the hot springs make part of the present communications. The examination of the Red River itself is but now commencing.
Thomas Jefferson, Special Message Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/203804