Ngorongoro Conservation Area/World Heritage Site (2,045,200 acres) protects wildlife habitat as well as the rights of local Maasai who graze their livestock on about 75 percent of the area. Ngorongoro Crater, 12 miles wide, is the world's largest intact caldera. Before the cataclysmic collapse of its cone 2 million years ago, this volcanic mountain may have been taller than Kilimanjaro. Its rim, which averages 7,600 feet elevation, is cloaked in moist montane forest and grassland, hosting elephants, golden-winged and eastern double-collared sunbirds, stonechats and Jackson's widowbird. From lodges and campsites on the rim, visitors are driven down to the crater floor for a 6-hour survey. At 5,600 feet elevation, the crater floor is primarily grassland, with patches of spring-fed marshes, freshwater ponds, a salt lake, and small forests. Harboring 20,000 large animals, it is a virtual Noah's Ark(without giraffes). Great effort has gone into saving the black rhino here, and several dozen are resident and counted from the air every night. Buffaloes, wildebeests, zebras, gazelles, and hartebeests graze the grassland, while elephants roam the wooded areas, and hippos gather in marshes and ponds. Lions, spotted hyenas, and golden and black-backed jackals are easy to find, but servals and cheetahs are sighted rarely. Resident ostriches, crowned cranes, and kori bustards are joined seasonally by migrant flocks of white and Abdim’s storks. The conservation area also includes two other voluminous craters, six peaks that top 10,000 feet and the southeastern corner of the vast Serengeti Plains. Ol’duvai Gorge, just north of the road to the Serengeti, has yielded hominid fossils key to the study of human evolution. Here sits a museum and shaded picnic sites. Red-and-yellow barbets join less colorful birds here for crumbs, while cheetahs sometimes roam nearby.