"The" Great Smoky Mountains
Not to get too technical here, but the article "the" would be appropriate to describe the "smokie" mountains:
"An article is a word that combines with a noun to indicate the type of reference being made by the noun. The three main articles in the English language are the, an and a. An article is sometimes called a noun marker, although this is generally considered to be an archaic term.
It is sometimes wondered which part of speech articles belong to. Despite much speculation, articles are not adjectives, as they do not describe nouns; THEY JUST AGREE WITH THEM. " (Wikipedia)
One does not go to Grand Canyon (there are places called this), they go to THE Grand Canyon. One does not go to THE Yellowstone National Park, because "THE" does not agree with it ;-)