In place names, do the words qualifying the place act as an adjective?

If you have a place name such as “The Sierra Nevada Mountains”, does Sierra Nevada act as an adjective? My guess is yes, since they qualify the noun mountains, e.g.: “Which mountains? The Sierra Nevada mountains.” (analogous to “Which dress? The red dress.”)

Likewise for places derived from that such as “The Sierra Nevada Lodge” — does Sierra Nevada act as an adjective there as well?

Solution 1:

Nouns Modifying Other Nouns

Your question is unclear.

If you are asking whether the noun is modifying another noun, then the answer is yes — but you knew that already or you would not have used the word “qualifying”. Modifying and qualifying are equivalent here.
If the question is whether a noun that modifies another noun thereby becomes an adjective, the answer is no, that does not make it an adjective.

A noun that modifies another noun remains a noun. Nouns can be modified by various sorts of things, and they are not all of them adjectives. Adjectives, however, can only be modified by adverbs.

As Professor Lawler observes, this works just like cheese in cheese sandwich, both of which are still nouns:

If cheese were an adjective in cheese sandwich, it would have properties of an adjective like being gradable and accepting adverbs as modifiers.
If cheese were a noun in cheese sandwich, it would have properties of a noun like accepting adjectives as modifiers.

Let’s put these to the test. Several, in fact.

Tests

Gradability Test

Let’s try inflecting cheese sandwich into the comparative and superlative degrees:

I would prefer a *cheeser sandwich.
Is that the *cheesest sandwich you have?

Nope: those are both ungrammatical.

Now try it with cheesy, which actually is an adjective:

I would prefer a cheesier sandwich.
Is that the cheesiest sandwich you have?

Notice those both work.

Adverb Application Test

One modifies adjectives with adverbs. Let’s try a few adverbs with cheese sandwich and see what happens:

I’d like a *very cheese sandwich.
I’d like a *really cheese sandwich.
I’d like an *always cheese sandwich.
I’d like a *carefully cheese sandwich.
I’d like a *lightly cheese sandwich.

Those all fail. In contrast, those tests work perfectly well with a real adjective:

I’d like a very cheesy sandwich.
I’d like a really cheesy sandwich.
I’d like an always cheesy sandwich.
I’d like a carefully cheesy sandwich.
I’d like a lightly cheesy sandwich.

Adjective Application Test

If cheese is not an adjective but rather a noun in cheese sandwich, then it should accept adjectives modifying it. Let’s try that:

I’d like a moldy cheese sandwich.
I’d like a melted cheese sandwich.
I’d like a rotten cheese sandwich.

Those work fine, producing sandwiches of moldy, melted, and rotten cheese respectively.

When it isn’t clear which of the two nouns the adjective is supposed to apply to, use a hyphen to clarify:

I’d like a rotten-cheese sandwich. (one made of cheese that’s gone off)
I’d like a rotten cheese-sandwich. (just a lousy sandwich overall)

Summary

Nouns that modify other nouns pass noun tests and fail adjective tests.

Therefore they are nouns, not adjectives.