Precambrian Formations and Precambrian History in Cochise County, Southeastern Arizona

Precambrian rocks of southeastern Arizona typically are exposed in isolated masses in a number of the tectonically complex ranges of the southern Basin and Range province. Preservation of original sedimentary and igneous textures and structures is commonly excellent, but the combination of extended Precambrian histories, discontinuous exposure and variable overlay of Mesozoic and Cenozoic deformation, magmatism and metamorphism provides major challenges for regional Precambrian correlations and historical interpretations. For all of the problems, however, the early work of F. L. Ransome (1903, 1904, 1915, 1919, 1923, and elsewhere) and N. L. Darton (1924, 1925) successfully established a basic Precambrian stratigraphic framework for this region which subsequent studies have refined but not replaced.