The geomorphology and late Cenozoic geology of a 71,500 square kilometer (27,600 square mile) area of northwestern Chihuahua and adjacent parts of Sonora, New Mexico and Texas are discussed. Emphasis is on description of three major physiographic units: The Sierra Madre Occidental, and two subsections of Mexican Basin and Range section. Formal names are proposed for the latter two subdivisions. The larger unit is characterized by broad desert basins and isolated ranges of northern and eastern Chihuahua and is designated the Bolson Subsection. The higher unit, designated the Babicora-Bustillos subsection, occupies a region that is transitional, in terms of terrain and geologic features, between the Bolson unit and the Sierra Madre. Physiographic boundaries were selected on the basis of study of recently-compiled 1:250,000 scale topographic maps and some field work. Control in the northern part of the area was also provided by photos taken from Apollo and Gemini spacecraft. Studies of basin- and valley-fill geology and geomorphology in the New Mexico-Chihuahua border region since 1950 have resulted in considerable elaboration of basic concepts of the late Cenozoic landscape evolution developed notably by Hill, Lee, Baker, Bryan and P. B. King. The fundamental concept of mid- to late Tertiary and Quaternary development and filling of intermontane basins, followed by local establishment of the entrenched Rio Grande Valley system during mid- to late Pleistocene time, appears to be generally applicable to the Basin and Range area under discussion. The important influence of a cyclic climatic change during the Quaternary period on landscape evolution is also recognized.