The Kalahari Desert is a large arid to semi-arid sandy area in southern Kgalagadi Africa extending 900,000 km² (362,500 sq. mi.), covering much of Botswana and parts of Namibia and South Africa, as semi-desert, with huge tracts of excellent grazing after good rains. The Kalahari Desert is the southern part of Africa, and the geography is a portion of desert and a plateau. The Kalahari supports some animals and plants because most of it is not true desert. There are small amounts of rainfall and the summer temperature is very high. It usually receives 3-7 1/2 inches of rain per year. Mary Sadler-Altena, "Kalahari: Introduction" webpage: blank">SouthernCape-Kalahari : Kalahari name/climate/reserves and history. The surrounding Kalahari Basin covers over 2.5 million km² extending farther into Botswana, Namibia and South Africa, and encroaching into parts of Angola, Zambia and Zimbabwe. The only permanent river, the _Okavango, flows into a delta in the northwest, forming marshes that are rich in wildlife. Ancient dry riverbeds—called omuramba—traverse the Central Northern reaches of the Kalahari and provide standing pools of water during the rainy season. Previously havens for wild animals from elephant to giraffe, and for predators such as lion and cheetah, the riverbeds are now mostly grazing spots, though leopard or cheetah can still be found.