desert muhafazah (governorate) of Egypt that includes all of Egypt west of Al-Jizah governorate and north of latitude 2620' N. Only one percent of its area is inhabited. It is mostly a plateau area of sedimentary rock such as limestone, averaging 700-800 feet (215-245 m) in elevation and nowhere surpassing 1,500 feet (460 m). Surface dissection results from wind erosion on the stone-covered wastes and sandy plains. Longitudinal belts of parallel sand dunes occur, rising to 200 feet (60 m) in the Great Sand Sea extending south from the Siwa Oasis. Light rain falls only along the coastal plain, but underground aquifers provide water for Siwa Oasis. The Qattara Depression reaches 435 feet (133 m) below sea level and occupies 7,000 square miles (18,000 square km), extending southward 35 miles (56 km) from the coast at Al-'Alamayn.
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