It's pretty difficult to deem Gutzon Borglum's initial vision for his colossal sculpture very feasible, considering it took over 14 years and nearly a million dollars just to carve out the presidents' faces! Regardless, a lack of funding forced the project to be scaled back to include only the heads of the former heads of state. This is probably a good thing though, because this preliminary design would have called for a sculpture well over 200 feet high. Oh, and if you're worried about the potential deterioration of this beloved national landmark, fear not - its estimated erosion rate is one inch every 1,000 years, so this mountain isn't due to be 'defaced' anytime soon!
Sources: (1, 2)
19 Astonishing Facts