The western part of the mountain range belongs mainly to the Pacific region, with the San Juan River standing out, while the eastern part belongs mainly to the Cauca River basin. The northern part and northwestern part belong to the Atlantic Slope, with the Atrato and Sinú rivers standing out. The Cordillera Occidental is separted from the coastal Baudó Mountains by the Atrato River.
The maximum altitude of the Cordillera Occidental can be found in the Farallones de Cali at 4,100 meters over sea level.