The Pacific Railroad surveys were some of the most important railway surveys ever undertaken in North America. Conducted from 1853 to 1855, the purpose of these surveys was to explore possible routes for the building of a transcontinental railroad, spanning the country from coast to coast. The discovery of gold and resulting rise in California's population beginning in the late 1840s made such a route essential in linking the country together. Though Congress had deemed this project necessary, there was much debate over where it should be built, and which states it would traverse.

In all, five separate surveys were conducted, each overseen by Jefferson Davis, then the Secretary of War, and conducted by the Corps of Topographical Engineers, a group which had already participated in surveys of the U.S.-Mexico border among other important surveys in the American West.

These surveys not only examined the land, but also consisted of a substantial survey of natural history, including geology, botany, and thousands of illustrations of birds, reptiles, amphibians, and mammals, as well as ethnographic descriptions of native tribes encountered by surveyors in the relatively unexplored West. These reports show just how varied a surveyor's job in this era could be.

Each of the five surveys explored one possible east-west route for railways, beginning roughly at the Mississippi River. The Northern Pacific survey was conducted along the Missouri River and over the Northern Rockies, between the 47th and 49th north parallels from St. Paul, Minnesota, all the way to the Puget Sound. The Central Pacific survey was conducted between the 37th and 39th parallels north, between St. Louis, Missouri and San Francisco, California, with a route following the Kansas and Arkansas Rivers. Two Southern Pacific Surveys were undertaken. The first followed the 35th parallel north from Oklahoma to Los Angeles; this route would be similar to the later Santa Fe Railroad line and the Interstate 40 highway. The second Southern Pacific Survey crossed Texas to San Diego, California. This route would become Southern Pacific's second transcontinental railway when it was completed in 1881. The final survey connected San Diego to Seattle for a coastal railway route.

Each of the survey routes posed its own challenges for the building of a railway. Obstacles included the Rocky Mountains and the Sierra Nevada, as well as thick growths of trees, rivers, and native tribes who would be hostile to the building of a railroad over their traditional lands. Even after the surveys were complete, there was great question over the most practical route in terms of both length and expense. Eventually, the line included over eight thousand feet of tunnels through the mountains, an impressive feat of surveying and engineering.

By the time the survey results were published in 1861, the country was embroiled in Civil War, drawing the nation's attention away from the railroad question and driving up the price of the equipment and materials necessary to build the rail line. Although the railway got off to a slow start, in July of 1862 Abraham Lincoln signed the Pacific Railway Act, establishing the Union Pacific Railroad Company to build west from Omaha, Nebraska, and the Central Pacific Railroad Company to build east from Sacramento, California. The companies building these lines received 33 million free acres of land along the new railroad. Construction began in 1863, with the two railways finally meeting each other in May of 1869 in Promontory, Utah. In all, this transcontinental railroad spanned 1,774 miles, a route which could be traveled in just over four days.