Principal Cordillera

[1] It extends in a north–south direction in the Argentine provinces of La Rioja, San Juan and Mendoza and the Chilean regions of Valparaíso, Santiago, O'Higgins and Maule.

Today these sequences of sedimentary and volcanic rock can be observed high in the Andes, implying their basin was closed and uplifted by tectonic inversion.

[4] Subsequent river incision shifted the divide to the east leaving old flattish surfaces hanging.

[4] The Principal Cordillera had risen to heights that allowed for the development of valley glaciers about 1 Ma ago.

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Nevado del Plomo (left) and Nevado Juncal (behind) are two mountains of the Principal Cordillera along the Argentina-Chile border and the Atlantic-Pacific watershed.