This seems to be a very early edition of a map that was issued as a base map for more than 20 years and was later reprinted in 1975.
Includes a Note. This map is mainly reduced from the official map, compiled in the Office of Explorations to exhibit Pacific Rail Road Routes, War Dept., and from Colton's Maps of the several states"
The map provides a highly detailed study of the various rivers draining into the Mississippi River, based upon the most up to day information.
The map includes red overprinting, noting annual rainfall.