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The twelve-volume work Reports of Explorations and Surveys to Ascertain the Most Practicable and Economical Route for a Railroad from the Mississippi River to the Pacific Ocean, commonly known as the U.S. Pacific Railroad Surveys, stands as one of the most comprehensive and ambitious survey projects of 19th-century America. Conducted between 1853 and 1855, the surveys were commissioned by the U.S. War Department to explore and document potential routes for a transcontinental railroad. The project was of immense logistical scale and engaged some of the foremost scientists, engineers, and cartographers of the period. Their work provided a meticulously detailed examination of the topography, geology, natural resources, and native populations of the vast western territories, producing a landmark study that shaped the expansion of American infrastructure and industry.

The U.S. Pacific Railroad Surveys encompassed five major exploratory routes across the western United States, each corresponding to different potential paths for the transcontinental railroad. These included surveys through the northern territories from the Great Lakes to Puget Sound, central and southern routes traversing the Rocky Mountains and Sierra Nevada, and a route running along the 32nd parallel near the Mexican border. The selection of these corridors was strategic, aimed at finding the most feasible passages across the varied landscapes while balancing the interests of northern, southern, and western states and territories. The territories explored ranged from the Great Plains, stretching through rugged mountain passes, to the arid deserts of the Southwest and the coastal lowlands along the Pacific, all meticulously recorded in reports, sketches, and maps.

The northernmost route, surveyed by Governor Isaac I. Stevens of Washington Territory, investigated a path from St. Paul, Minnesota, across the northern plains, through the Rocky Mountains at Marias Pass, and to Puget Sound.  Stevens’ survey is especially notable for its contributions from naturalists like George Suckley and John G. Cooper, who meticulously cataloged the flora and fauna encountered. Additionally, Stevens was a proponent of indigenous cooperation, advocating negotiations with Native American tribes to establish safe passage along the proposed route.

In the central region, John W. Gunnison led an expedition through the 38th parallel, traveling from St. Louis across Kansas and Colorado, into the rugged terrain of Utah, and finally into the Sierra Nevada. Tragically, Gunnison was killed during a skirmish with local Native Americans, and the survey was completed by Lieutenant Edward Griffin Beckwith. Gunnison and Beckwith’s reports are particularly valuable for their surveys of the Wasatch Range and for the inclusion of detailed maps that influenced later routes through the Great Basin and Salt Lake Valley.  

Further south, the survey of the 35th parallel was led by Lieutenant Amiel Weeks Whipple, who documented the region extending from the Arkansas River through New Mexico and Arizona to the Pacific Ocean. Whipple’s route traversed desert regions and rugged landscapes, including the Colorado River basin. Whipple's survey also notably included artists like Heinrich Balduin Möllhausen, whose depictions of the landscapes and indigenous communities provided visual insights that were critical for Eastern audiences.

The southernmost route, following the 32nd parallel along what would become the Southern Pacific Railway corridor, was led by John Pope and pursued a path from the Red River to the Rio Grande and through Arizona and Southern California. This survey was strongly supported by Southern legislators, as it followed a path that could support a southern transcontinental link and presented fewer winter weather challenges compared to the northern routes. The reports from this route highlighted the unique topography of the Sonoran Desert and the California coastal plains.  

In addition to the geographic explorations, the project saw significant contributions from leading cartographers and naturalists who produced groundbreaking work in mapmaking and scientific documentation. The primary cartographer was Lieutenant Gouverneur K. Warren, who oversaw the integration of the collected data into comprehensive maps. Warren's meticulous maps synthesized data from all five routes, resulting in the production of some of the most accurate and detailed maps of the American West at the time. His work was instrumental in consolidating information on the vast, uncharted territories, transforming raw survey data into accessible and invaluable resources for future expeditions and developments.

Several artists, including Möllhausen and F.W. Egloffstein, a German-born topographer, provided a visual dimension to the Pacific Railroad Surveys. Egloffstein’s contribution was pioneering; he used photolithography to create shaded relief maps, an innovation that added depth and realism to the depictions of the western terrain. His maps, particularly of the Great Basin, are considered some of the earliest examples of printed relief maps, giving readers in the East a tangible sense of the rugged landscapes and the formidable task of constructing a railroad through such regions. 

The Pacific Railroad Surveys ultimately represented a collaborative effort that blended military precision, scientific rigor, and artistic skill to document the vast American landscape. While the route eventually chosen for the transcontinental railroad would follow a central corridor through Wyoming, the surveys influenced the development of future transportation corridors and provided foundational knowledge about the American West.