Richard Ford, the 19th century traveller and first British hispanophile, jokingly said in 'Gatherings from Spain' that the country is just one big mountain. 24% is above 1000 m and 76% between 500 and 1000 m. Spain has an average altitude of 660 metres. In Europe only Switzerland is higher (by a long way - average altitude of 1,300 metres).
So it should come as no surprise that Castilian is so rich in words for mountains, hills, cliffs and plateaus. Here's a by no means exhaustive list. See also Mountains in Spain
alcarria: high-flat plateau with little vegetation.
aguja: jagged peak
altiplanicie: extensive high plateau
altiplano: synonym of altiplanicie
altozano: small hill
arista: ridge; arête
cerrajón: steep, high cerro.
cerrejón: small cerro.
cerro: isolated hill
collado: highland; hill; mountain pass
cornisa: ridge; clifftop; crag.
cordillera: mountain range
cresta: ridge; arête; crest
crestón: crag; small crest.
cuerda: ridge of peaks
cueto: isolated, craggy, cone-shaped hill
derrumbe: cliff (off which it is easy to fall)
desgalgadero: steep scree slope; cliff
despeñadero: cliff; precipice.
escarpa: escarpment; scarp; slope
estribaciones: foothills; spurs
farallón: cliff, headland, outcrop
galayo: jagged rock sticking out from a mountainous area
hacho: large prominent hill; beacon hill.
loma: hill; low ridge.
meseta: extensive, flat or gently-undulating land higher than surrounding areas.
moheda: high hill with scrub vegetation
monte: hills; mountains; hill
muela: mound; steep hill
otero: hill, viewpoint
pena (Gal.): crag
penya (Cat.): crag
peña: cliff; crag
peñascal: rocky place; rocky hill.
peñón: mass of rock. El Peñón - the Rock (of Gibraltar)
picacho: jagged peak
pueyo: isolated hill rising above a plain
risco: cliff; crag
sierra: hill range; hills; sierra
teso: low flat-topped hill
tolmo: large rock; crag
tozal: summit of a hill from which there is a view of the surrounding area
Things on the ground become even more complicated when one considers the Basque, Catalan and Galician (along with all the others) names for these things.