Reports of Explorations and Surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean

With the enormous territorial gains from the Mexican-American War (1846–1848) and the Gadsden Purchase (1854), the United States was presented with new possibilities for finding a western route to complete a transcontinental railroad. The Army’s engineers preferred a southern route along the new border with Mexico because it offered optimal climate for year-round travel. Northerners, however, wanted a route closer to the Oregon Trail. To settle the matter, Secretary of War Jefferson Davis authorized a survey of four possible routes.

Surveys were conducted by the U.S. Army Corps of Topographical Engineers between 1853 and 1855. In addition to the engineers, these expeditions included scientists, naturalists, artists, and draftsmen to make a record of the terrain and its inhabitants. As some of the proposed routes passed through relatively unexplored territories, the final reports described not only the surveyed routes but also illustrated and reported on natural history—geology, paleontology, plants, animals, and descriptions of the native peoples living in the territory.

The best documented survey expedition followed the 35th parallel from Oklahoma, into New Mexico, Arizona, and Southern California. The botanical report for this survey included a section on Cactaceae by George Engelmann, the St. Louis physician and botanist who had authored a similar report for the U.S.–Mexican Boundary Survey; his report includes 24 highly detailed illustrations by Paulus Roetter. The botanical report by John Torrey, the Princeton botanist, includes 25 excellent illustrations but no indication of the illustrator. In both reports the engravings were prepared by the master lithographer Joseph Prestele.

The final survey reports were published between 1855 and 1860 and comprised 12 volumes that presented a mountain of scientific reports and an impressive number of illustrations. The information gathered by the engineers and naturalists was of sufficient quality as to be studied by American and European scholars for many years thereafter.