The Nile Valley, including the delta, is Egypt's most notable physical feature. For thousands of years this narrow, densely settled ribbon of land, with its fertile soils and its reliable supply of water, has nurtured Egyptian civilization. South of Cairo, in the area known as Upper Egypt, the valley varies from 1 to 13 miles (1.6 to 21 km) in width and in many places is flanked by high cliffs. North of Cairo, in Lower Egypt, the flat delta begins; it gradually fans out to a maximum width of about 150 miles (240 km) along the Mediterranean coast.
West of the Nile Valley are the vast tracts of sand, shifting dunes, gravel, and rocky outcrops that make up the Western and Libyan deserts. Here, too, are scattered oases, chief of which are the Faiyum, Bahariya, Farafra, Dakhla, Kharga, and Siwa oases. Elevations throughout the west are generally less than 1,000 feet (300 m) above sea level. On the Gilf Kebir Plateau, in the southwest, they reach more than 3,300 feet (1,000 m). There are also scattered areas of below-sea-level land in the west. The Qattara Depression, at the edge of the Libyan Plateau, descends to 436 feet (133 m) below sea level, one of the lowest points in Africa.
East of the Nile is the Eastern Desert. It consists mainly of desolate, rough plateaus rising gradually eastward and reaching their greatest height in mountainous areas near the Red Sea coast. A few peaks rise 5,000 to 7,000 feet (1,500 to 2,100 m) above sea level.
The Sinai Peninsula, a triangular block of land, has terrain resembling that of the Eastern Desert. It is highest and most rugged in the south. Mount Katherina rises here to 8,652 feet (2,637 m), which is Egypt's highest point. Elevations decline northward in the Sinai as the land gradually flattens and becomes sandy desert along the Mediterranean coast.
The Nile, fed by countless streams originating in the more humid parts of Africa, is Egypt's only river and the source of practically all its water. Elsewhere, there are only wadis, stream beds that are dry except for brief periods following rare thunderstorms in the desert. Limited amounts of subterranean and artesian water are available in the scattered oases.