The main feature of the NCA is the Ngorongoro Crater, a large, unbroken, unflooded volcanic caldera. The crater, which formed when a giant volcano exploded and collapsed on itself some two to three million years ago, is 610 m (2,000 ft) deep and its floor covers 260 km2 (100 sq mi).[5] Estimates of the height of the original volcano range from fifteen to nineteen thousand feet (4500 to 5800 metres) high.


http://en.wikipedia.org/wiki/Ngorongoro_Conservation_Area