In pursuance of a measure proposed to Congress by a message of Jan. 18. 1803. and sanctioned by their appropriation for carrying it into execution, Capt Meriwether Lewis of the 1st. regiment of infantry was appointed, with a party of men, to explore the river Missouri, from it’s mouth to it’s source, &, crossing the highlands by the shortest portage, to seek the best water communication thence to the Pacific ocean; & Lieutt. 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 Nov. took up their winter quarters near the Mandan towns, 1609 miles above the mouth of the river, in Lat. 47°.21’-47" North, & Long. 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 Apr. 7. from Capt. Lewis, is herewith communicated. during his stay among the Mandans, he had been able to lay down the Missouri, according to courses & distances taken on his passage up it, corrected by frequent observations of Longitude & Latitude, & to add to the actual survey of this portion of the river, a general map of the country between the Missisipi & Pacific, from the 34th. to the 54th. degrees of Latitude. these additions are from information collected from Indians with whom he had opportunities of communicating during his journey & 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, & the countries adjacent to it’s Northern and Western borders, of their commerce, & of other interesting circumstances respecting them.

In order to render the statement, as compleat as may be, of the Indians inhabiting the country West of the Missisipi, I add Doctr. Sibley’s account of those residing in & 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 & valuable services in the prosecution of these enterprizes. he ascended the river to the remarkeable Hot springs near it in Lat. 34°.31’-4.16" Long. 92°50’-45" West from Greenwich, taking it’s courses & distances, & correcting them by frequent celestial observations. Extracts from his observations, and copies of his map of the river, from it’s mouth to the Hot springs, make part of the present communications. the examination of the Red river itself, is but now commencing.