The Jordan Valley has a maximum depression of 392 m (1,286 ft) below sea level at the Dead Sea; south of the Dead Sea the depression, called Wadi'Araba, slowly rises to reach sea level about halfway to the Gulf of Aqaba. To the east of the Jordan River, the Transjordanian plateaus have an average altitude of 910 m (3,000 ft), with hills rising to more than 1,650 m (5,400 ft) in the south. Farther eastward, the highlands slope down gently toward the desert, which constitutes 88% of the East Bank. The Jordan River enters the country from Israel to the north and flows into the Dead Sea; its main tributary is the Yarmuk, which near its juncture forms the border between Jordan and Syria. The Dead Sea is the lowest point on the earth's surface, at 408 m (1,339 ft) below the level of the Mediterranean. The Dead Sea has a mineral content of about 30%.