Sierra Madre Occidental vs chain of mountains

Sierra Madre Occidental and chain of mountains both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sierra Madre Occidental	Yes	No	No	No
chain of mountains	Yes	No	No	No

Sierra Madre Occidental (noun)	chain of mountains (noun)
a mountain range in northwestern Mexico that runs south from Arizona parallel to the Pacific coastline	a series of hills or mountains