The Great Rift Valley is a geological fault line 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 Ethopia. It was formed on the "Kenyan Dome" a geographical upwelling created by the interactions of three major tectonics: the Arabian, Nubian, and Somalian plates.
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 fertile soils from relatively recent volcanic activity.
Main lakes in the rift are Lake Turkana, Lake Logipi, Lake Bogoria, Lake Baringo, Lake Naivasha, Lake Nakuru, Lake Elementaita Lake Magadi are some of the lakes found in the area. Of these eight, only Lakes Baringo and Naivasha are fresh water.
The Elgeyo escarpment forms part of the western wall. The Kerio Valley lies between the Tugen Hills and the Elgeyo escarpment. Further south the Mau Escarpment is a steep natural cliff approximately 3,000 m (10,000ft) high, running along the western edge of the Great Rift Valley about L Naivasha. Further south the Nguruman Escarpment is around 50 kilometers long and elongated in N-W direction. Its northern edge is about 120 kilometres (75miles) southwest of Nairobi, while the southern edge is near the Tanzanian border, at the northwestern corner of Lake Natron. The Aberdare Range forms a section of the eastern rim of the Great Rift Valley to the north of Nairobi. Mount Satima lies at the northern end of the Aberdares and is their highest point, and Mount Kinangop at the southern end is the second highest. The mountains form a ridge between these two peaks. Ngong Hills are peaks in a ridge along the east of the Great Rift Valley, located southwest near Nairobi.