The Great Rift Valley is a large trough that runs through Kenya from north to south. It is part of the Gregory Rift, the eastern branch of the East African Rift, which starts in Tanzania to the south and continues northward into Ethiopia. In the past, it was seen as part of a "Great Rift Valley" that ran from Madagascar to Syria. Most of the valley falls within the Rift Valley Province.
The valley contains the Cherangani Hills and a chain of volcanoes, some of which are still active. The climate is mild, with temperatures usually below 28 °C (82 °F). Most rain falls during the March–June and October–November periods. The Tugen Hills to the west of Lake Baringo contain fossils preserved in laval flows from the period 14 to 4 million years ago. The relics of many hominids, ancestors of humans, were found here.
The valley is bordered by escarpments to the east and west. The floor is broken by volcanoes, some still active, and contains a series of lakes. Some of the soils are Andisols, fertile soils from relatively recent volcanic activity.
Lake Turkana occupies the northern end of the Great Rift Valley in Kenya. The Suguta Valley, or Suguta Mud Flats, is an arid part of the Great Rift Valley directly south of Lake Turkana. The shield volcano Emuruangogolak straddles the valley to the south of Suguta, and further south Mount Silali and Paka rise from the valley floor. Paka is a shield volcano, with widespread geothermal activity. South of Paka are Mount Korosi, Lake Baringo and Lake Bogoria. Menengai is a massive shield volcano in the floor of the rift with a caldera that formed about 8,000 years ago. It overlooks Lake Nakuru to the south. This region also includes Lake Elementaita, Mount Kipipiri and Lake Naivasha.
The Hell's Gate National Park lies south of Lake Naivasha. In the early 1900s, Mount Longonot erupted, and ash can still be felt around Hell's Gate. Mount Longonot is a dormant stratovolcano located southeast of Lake Naivasha. Suswa is a shield volcano located between Narok and Nairobi. Lava flows from the most recent eruptions are still not convered by vegetation, and may be no more than one hundred years old. Lake Magadi is the most southern rift valley lake in Kenya, although the northern end of Lake Natron in Tanzania reaches into Kenya.
From north to south, the main lakes in the Kenyan Rift Valley are Lake Turkana, Lake Baringo, Lake Bogoria, Lake Nakuru, Lake Elmenteita, Lake Naivasha and Lake Magadi. Lakes Turkana, Baringo and Naivasha are fresh water. Lake Turkana, at the northern end of the rift, is 250 kilometres (160 mi) long, between 15 kilometres (9.3 mi) and 30 kilometres (19 mi) wide and is 125 metres (410 ft) at its greatest depth. Most of the other lakes are shallow and poorly drained, and therefore have become alkaline. They have waters that are rich in blue-green algae, which feed insect larvae, small crustaceans and Lesser Flamingos. The larvae and crustaceans are food for fish and Greater Flamingos. Trona, used for sodium carbonate production, has been mined at Lake Magadi for nearly 100 years.
Three shallow alkaline lakes and the surrounding lands make up the Kenya Lake system: Lake Bogoria at 10,700 hectares (26,000 acres), Lake Nakuru at 18,800 hectares (46,000 acres) and Lake Elementaita at 2,534 hectares (6,260 acres). This system has one of the most diverse populations of birds in the world, and is the home of thirteen globally threatened species of bird. It is an important nesting and breeding site for Great White Pelicans, and is the most important feeding area for lesser flamingos in the world. The system is home to globally important populations of Black-necked Grebe, African Spoonbill, Pied Avocet, Little Grebe, Yellow-billed Stork, Black-winged Stilt, Grey-headed Gull and Gull-billed Tern.
The Kenya Lake system is a key location on the West Asian-East African Flyway, a route followed by huge numbers of birds in their annual migration from breeding grounds in the north to wintering places in Africa. The lands around the lakes include large populations of black rhino, Rothschild's giraffe, greater kudu, lion, cheetah and wild dogs. The Kenya Lake system is surrounded by the steep escarpment of the Rift Valley, which provides a spectacular backdrop. Other lakes are Lake Chew Bahir, in the northeast extension. This lake lies mainly in Ethiopia but extends into Kenya in the rainy season. Lake Kamnarok is a another small lake.