 The park is at an elevation of 1 @,@ 821 feet ( 555 m ) on the Allegheny Plateau , which formed in the Alleghenian orogeny some 300 million years ago , when Gondwana ( specifically what became Africa ) and what became North America collided , forming Pangaea . While the gorge and its surroundings appear mountainous , these are not true mountains : instead years of erosion have made this a dissected plateau , causing the " mountainous " terrain seen today . The hardest of the ancient rocks are on top of the ridges , while the softer rocks eroded away forming the valleys . 
