English: Drawn by Thomas Jekyll. Lithographed by Sarony, Major, & Knapp.

The science of geology was a controversial subject in the nineteenth century. People argued over geological timelines that seemed to conflict with some long-held religious beliefs grounded in literal interpretations of ancient scriptures. Although somewhat fanciful and based upon incomplete data, James Hall and Peter Lesley's map appearing in volume one of the Boundary Survey report was the first American attempt at a comprehensive geological surface map of the trans-Mississippi West. Hall was a leading geologist and paleontologist in Albany, New York, and he trained a number of the scientists who participated in the later western surveys. He did not accompany the U.S.-Mexican Boundary Survey in the field but examined and studied the geological specimens brought back east by expedition members Dr. Charles C. Parry, assistant computer, geologist, and botanist, and Arthur Schott, surveyor, topographer, artist, and naturalist. Hall supplemented their geological reports by writing his own from a paleontological perspective, that is, by using fossils found in various strata to help construct a geological history of the West. These studies, Emory's survey maps, Pacific Railroad survey maps, and information and specimens collected by other surveys formed the basis of the map. Unlike nearly all of these other survey maps, this one appeared in multiple colors. The style of coloring in this chromolithograph resembles that of William Smith's grand (six-by-nine-foot) hand-colored Geological Map of England and Wales and Part of Scotland, produced by John Cary in 1815-1817, which has been recently called "The Map That Changed the World" based on the revolution in scientific thought that it represented. Hall and Lesley's map was not quite as revolutionary, but it beautifully demonstrated advances in American scientific knowledge. By omission, the blank areas in the far west on the map also indicated areas for which little or no data existed. The map's focus on stratigraphy rather than information such as mineral deposits reflected the interests of Eastern intellectuals rather than Western developers.