This comprehensive monograph features detailed findings from the University of Michigan's 1930 expedition to the San Carlos Mountains in Tamaulipas, Mexico. Directed by Lewis Burnett Kellum, the team included Harley H. Bartlett, Edson S. Bastin, Lee R. Dice, Ralph W. Imlay, George W. Rust, and Edward H. Watson. The report was published in 1937 by the University of Michigan Press. The field work began in May 1925, with a reconnaissance survey by Lewis B. Kellum for the Standard Oil Company of New Jersey. The expedition aimed to study the geology and biology of the region, and its outcomes are documented in this volume. The content is spread across various chapters, covering the geology of sedimentary and igneous rocks, ore deposits, and the Sierra de Cruillas. It also includes detailed studies on the mammals, tarantulas, fishes, amphibians, and reptiles of the area. The introduction outlines the historical context, mapping methodology, and the acknowledgment of individuals and organizations that facilitated the expedition. The report includes illustrations and maps, offering a thorough scientific investigation of the San Carlos Mountains.