The
Kerio River binds the county on the eastern side. From its
alluvial plain, the
topography gradually rises towards the west. The
Elgeyo Escarpment stands out distinctly with elevation differences of up to 1,500 metres. In the northern and southern parts of the county the topography is rugged, giving way to more subdued relief differences going westwards. The underlying
geology consists of
gneisses from the Basement System. The
Cherangany Hills rise gently to form the western half of the
Great Rift Valley and extend northwest in a broken chain to
Mount Moroto in
Uganda. Non-volcanic in origin, the Cherangany Hills resulted from subsequent erosion of the raised western ridge of the
Eastern Rift Valley. The range is approximately long and wide and averages in height; the highest point is more than . Many of the summits are covered with huge groundsels and
lobelias. Some of the hills include Kamologon (3581 m), Chebon (3375 m), Chepkotit (3370 m), Karelachgelat (3350 m) and Sondany (3211 m). == Climate ==