The first Disneyland roller coaster was the Matterhorn, built to resemble the actual mountain found in the Alps. So, since then, the major Disney attractions of significant size, mostly roller coasters, all were given the name “mountain.” Some of them, like Thunder Mountain Railroad, make some sense, as there is an actual, albeit scaled-down, mountain in the attraction. But what exactly is a Space Mountain anyway? Clearly the only reason it has that name is that it’s a large roller coaster. The coaster itself is the “mountain.”
Article source: https://www.cinemablend.com/news/2557522/5-things-disneys-space-mountain-movie-needs-to-include