This is the 12583rd most frequent Spanish word.
montañoso
Mountainous.
The term 'montañoso' describes the quality of having many mountains.
El paisaje montañoso es impresionante.
The mountainous landscape is breathtaking.
Here, 'montañosa' qualifies 'región', indicating that the region contains mountains.
Viajaron por una región montañosa durante sus vacaciones.
They traveled through a mountainous region during their vacation.
In this case, 'montañosa' modifies 'zona', referring to its nature as containing mountain terrain.