Chile’s Norte Grande boasts three ecological strata: the coast, the Pampa or desert, and the Puna or Altiplano. The last of these is further divided into the Puna Seca (dry Puna), which stretches from Arica to Iquique and is humid enough to allow for agriculture, and the Puna Salada (salty Puna), which runs from Iquique to the Atacama Salt Flat and where conditions are so harsh that human occupation is impossible most of the year. For its part, the desert Pampa is scored by valleys and ravines in the far north, then gives way to the Tamarugal Pampa, with its vast forests of tamarugo, chañar and algarrobo. South of the Loa River is the absolute desert. On the coast, in contrast, both the climate and resources available are much more stable.