Ethiopia is bounded by Eritrea to the north, Djibouti to the northeast, Somalia to the east, Kenya to the south, and South Sudan and Sudan to the west. Ethiopia’s topography, one of the most rugged in Africa, is built on four geologic formations. Rocks of Precambrian origin (more than 540 million years in age) form the oldest basal complex of Ethiopia, as they do in most of Africa. The Precambrian layer is buried under more recent geologic formations—except in parts of northern, western, and southern Ethiopia, where there are exposed rock layers of granite and schist. Geologic processes of the