The Pacific Railroad Surveys (1853–1855) were a series of explorations of the American West designed to find and document possible routes for a transcontinental railroad across North America. The expeditions included surveyors, scientists, and artists and resulted in an immense body of data covering at least 400,000 square miles (1,000,000 km2) on the American West. "These volumes... constitute probably the most important single contemporary source of knowledge on Western geography and history and their value is greatly enhanced by the inclusion of many beautiful plates in color of scenery, native inhabitants, fauna and flora of the Western country." Published by the United States War Department from 1855 to 1860, the surveys contained significant material on natural history, including many illustrations of reptiles, amphibians, birds, and mammals. In addition to describing the route, these surveys also reported on the geology, zoology, botany, paleontology of the land as well as provided ethnographic descriptions of the Native peoples encountered during the surveys.

The Central Pacific Railroad (CPRR) was a rail company chartered by U.S. Congress in 1862 to build a railroad eastwards from Sacramento, California, to complete most of the western part of the "First transcontinental railroad" in North America. Incorporated in 1861, CPRR ceased independent operations in 1875 when the railroad was leased to the Southern Pacific Railroad. Its assets were formally merged into Southern Pacific in 1959.