The Andes constitute Argentina's western boundary with Chile from latitude 22°50^prime South to latitude 50°48^prime South. The mountain belt of western Argentina consists of a series of sub-parallel chains, which decrease in number, width, and elevation from north to south. Although the Andes may be considered as a single geographic unit, they are formed by several different morphostructural elements orientated from north-northwest to south-southeast, and therefore oblique to the trend of the continental divide.

The various morphostructural elements which, from north to south, constitute the Chilean-Argentinian Andes, are as follows.

1. The high plateau of the Puna de Atacama, followed to the east by the Eastern Cordilleras (Prepuna) and the Subandean Ranges.
2. The Pampean Ranges.
3. The Precordillera of La Rioja, San Juan, and Mendoza.
4. The Frontal Cordillera.
5. The Main Cordillera.
6. The Patagonian Cordillera.

The extension and main stratigraphic and structural features of the different morphostructural elements, as well as the geologic evolution of western Argentina, are summarily described.