House of Representatives, 33rd Congress, 3rd Session, Executive Document 91. ""Report of Explorations for a Route for the Pacific Railroad, by Capt. J. W. Gunnnison, topographical engineers Near the 38th and 39th Parallels of North Latitude from the Mouth of the Kansas River, MO.,. to the Sevier Lake, in the Great Basin. Report by Lieut. E. G. Beckwith, Third Artillery.""
Jefferson Davis was Secretary of War at the time of the Survey expedition. A large number of issues surrounding the whole project existed still when he finally got appropriation to fund the project with the assistance of Senator Gwin, California. Some of the questions were: Where to build it? Where to begin and where to end? Which states to go through? As can be readily imagined the political and regional pressures were enormous.
Finally, four routes were selected to be explored. The one most favoured by Jefferson Davis himself was the fourth route from Texas along the Gila River to San Diego; another supported by Senator Thomas Hart Benton followed the Kansas River to Arkansas to Salt Lake along the 37-39th parallels. Yet another proposed "middle route" ran from Arkansas through across New Mexico and Arizona and finally crossed the Mojave Desert in California. The northernmost route proposed came along the Missouri River across the Northern Rocky Mountains to Puget Sound, staying along the 47-49th parallels. In addition, of course, there were surveys on the west coast suggesting routes to link San Diego, San Francisco and the Pacific Northwest.
When the reports were complete they encompassed much more than just a railroad survey, they also included natural history, topography and geology of the territories surveyed, and were amply illustrated with plates and maps. John M. Stanly was the most prominent of the eleven illustrators accompanying the expedition and he illustrated more plates than any of the others. The plates show scenery, native inhabitants, flora, fauna, archaeological interests, as well as numerous maps. There are also many plates of birds of all kinds. The reconnoisances made possible the first reasonably accurate topographical map of the West.
Published by the Federal Government, these reports provide the single most important contemporary source of knowledge for the geography of the West. The set is a corner stone work in a Western Americana collection and is considered one of the most important works on the Transmississippi West for its published reports on the explorations and the data collected during the surveys. [Wagner-Camp The Plains and the Rockies, p. 262].