Kerio Valley lies between the Tugen Hills and the Elgeyo escarpment at an elevation of 1,000 m. in the Great Rift Valley in Kenya. The valley lies in a narrow, long strip approximately 80 km by 10 km wide at its widest, through which the Kerio River flows. In Kimwarer in the southern part of the valley fluoride is mined by the Kenya Fluorspar Company. The southern parts of the valley are settled the Elgeyo people live, and the northern part by the Marakwet people. Tugen people live on the slopes of the Tugen Hills. These three groups belong together with the Nandi and the Kipsigis to the Kalenjin people.