While standing over 14,000 feet atop Mount Evans, the highest summit of the Front Range in Colorado, a rather breathless Tom Scott explained the process of prominence by which a mountain is determined to be a mountain rather than a hill.
…in formal terms, we solve it by measuring prominence. Prominence works like this: imagine if you could raise sea level up to where I’m sitting now. How many meters would it have to drop before you could connect this mountain to another, taller one and walk there without getting your feet wet? For Mount Evans, that is 839m down, or about one-fifth of its height above sea level.