The Cordillera Occidental () is the lowest in elevation of the three branches of the Colombian Andes. The average altitude is and the highest peak is Cerro Tatamá at . The range extends from south to north diverging from the Colombian Massif in Nariño Department, passes north through Cauca, Valle del Cauca, Risaralda, Chocó, and Caldas Departments to the Paramillo Massif in Antioquia and Córdoba Departments. The cordillera is paralleled on the east by the Cauca river. From this massif the range divides further to form the SerranÃÂas de Ayapel, San Jerónimo and Abibe, receding into the Caribbean plain and the Sinú River valley.
It is a direct continuation of the Cordillera Occidental of Ecuador.
The western part of the mountain range belongs to the Pacific region of Colombia, with the San Juan River being the main watershed, while the eastern part belongs to the Cauca River basin. The northern and northwestern parts belong to the Atlantic Slope, with the Atrato and Sinú Rivers being the main watersheds. The Cordillera Occidental is separated from the coastal Baudó Mountains by the Atrato River.
A number of ecoregions cover the cordillera. The ChocóâÂÂDarién moist forests cover the western foothills below 1000 meters elevation. The Northwestern Andean montane forests cover the humid western slopes of the range. The Cauca Valley montane forests cover the eastern slopes. Northern Andean páramo covers the highest elevations.
The West Andes have the following nationally protected areas from south to north:
Other areas under consideration for national protection include: