The Negev covers 55% of Israel. It has a number of interesting cultural and geological features, among them are 3 craterlike makhteshim (box canyons) which are unique to the region. The Negev can be split into 5 different ecological regions: northern (300mm of rain annually, fairly fertile soils), western (250mm of rain per year with light and partially sandy soils), and central Negev (annual precipitation of 200mm, with impervious soil allowing minimum penetration of water with greater soil erosion and water runoff), the high plateau (370-520m above sea level, gets 100mm of rain per year with inferior and partially salty soils) and the Arabah Valley (very arid with barely 50mm of rain annually. It has inferior soils in which little can grow without irrigation and special soil additives).