The Great Rift Valley, with its associated escarpments and mountains, is a major feature. It runs the length of the country from Lake Turkana in the north to Lake Natron on the southern border with Tanzania.The central portion of the rift is raised, with the Aberdare Mountains and Mt Kenya to the east and the Mau Escarpment and Cherangani Hills to the west. The northern and southernmost sectors of the rift are low-lying, arid and rugged, with spectacular volcanic landforms. The region west of the central highlands is characterized by Precambrian metamorphic rocks and linear basement hills. Mt Elgon, an old, eroded volcano, intrudes through the ancient shield on the Uganda border.