The Negev is a rocky desert. It is a melange of brown, rocky, dusty mountains interrupted by wadis (dry riverbeds that bloom briefly after rain) and deep craters. It can be split into five different ecological regions: northern, western and central Negev, the high plateau and the Arabah Valley. The northern Negev, or Mediterranean zone, receives 300 mm of rain annually and has fairly fertile soils. The western Negev receives 250 mm of rain per year, with light and partially sandy soils. Sand dunes can reach heights of up to 30 metres here. Home to the city of Beersheba, the central Negev has an annual precipitation of 200 mm and is characterized by impervious soil, known as loess, allowing minimum penetration of water with greater soil erosion and water runoff. The high plateau area of Negev Mountains/Ramat HaNegev (, The Negev Heights) stands between 370 metres and 520 metres above sea level with extreme temperatures in summer and winter. The area gets 100 mm of rain per year, with inferior and partially salty soils. The Arabah Valley along the Jordanian border stretches 180 km from Eilat in the south to the tip of the Dead Sea in the north. The Arabah Valley is very arid with barely 50 mm of rain annually. It has inferior soils in which little can grow without irrigation and special soil additives.