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This geological map, prepared by James Hall and J.P. Lesley, was created to accompany Report on the United States and Mexican Boundary Survey, Made Under the Direction of the Secretary of the Interior, by William H. Emory (1857–1859). It stands as one of the classic maps of Texas and Western history, offering a foundational geological survey of the trans-Mississippi West. Compiled from data gathered during Emory’s boundary survey—conducted to finalize the border following the Gadsden Purchase of 1853—the map represents a significant milestone in American geological and geographical studies.

As William Goetzmann notes, “On August 15, 1854, Major William H. Emory was ordered by the Secretary of the Interior to complete the marking of the United States-Mexican boundary subsequent to the Gadsden Purchase of 1853. In addition, he was ordered to make ‘an examination of the country contiguous to the line to ascertain its practicability for a railway route to the Pacific’ and also to collect information ‘in reference to the agricultural and mineral character of the country and its present occupants.’ The result of Emory's labors on this survey… were finally published in three massive volumes between 1857 and 1859. Emory’s Report was perhaps the most complete scientific description ever made of the lands, the people, and the border country.”

The geological section of the Report, which this map accompanied, was groundbreaking in its scope and synthesis. As Goetzmann further observes, “The geological section was the first attempt by reputable scientists to construct an all-over version of the trans-Mississippi geography… In addition to this the three geologists—Parry, Schott and Hall—attempted to derive causal principles from the mass of observed data and thus to reconstruct the geological history of the region.”

Beyond its scientific contributions, the map had immediate practical applications. Emory’s survey was not just an exercise in boundary demarcation but a broader effort to assess the region’s economic and strategic potential, particularly for railroad expansion. The Report and its maps informed federal policy and private investment, shaping the settlement and development of the American Southwest. Today, this map remains a landmark in both geological cartography and the history of Western exploration.