The Pacific Railroad Surveys (1853–1855) consisted of a series of explorations of the American West to find 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 illustration