The area is named after Ngorongoro Crater, a large volcanic caldera within the area. The Ngorongoro Conservation Area Authority administers the conservation area, an arm of the Tanzanian government, and its boundaries follow the boundary of the Ngorongoro District in Arusha Region. The western portion of the park abuts the Serengeti National Park, and the area comprising the two parks and Kenya's Maasai Mara game reserve is home to Great Migration, a massive annual migration of millions of wildebeest, zebras, gazelles, and other animals. The conservation area also contains Olduvai Gorge, one of the most important paleoanthropological sites in the world.