Although possessing a common physical heritage, the Sonoran Desert has taken on highly contrasting forms in its American and Mexican portions. This work does not, therefore, attempt a regional study in the usual sense of the term, but is rather an examination of disparate economic development, much influenced by contrasting technological achievements as well as the accidents of history.Although the significance of geographic regionalism is implicit throughout this study, no attempt is made to show any overriding unity at work, geographical or otherwise, welding together a "desert region." Instead the desert acts as a stage for social drama in which drought and extreme heat provide the essential backcloth. The scarcity of water and man's inability to grow crops without irrigation have not, indeed, changed with time, and only constant reference to this immutable factor can give meaning to the evolution of human activities within the desert.