Although, as in other physical or biogeographic aspects, heterogeneity is what predominates in Spanish soils in general they are not usually the most appropriate fit for agricultural use and need careful cultivation and irrigation systems. Moreover, when these soils are sufficiently rich and deep, they may see limited possibilities for other geographic variables. The steep slopes make the bare rock appears and the extreme dryness leaves a skeletal soils and almost no vegetation cover in areas such as the southeast and areas of the Ebro valley. In general we find rich soils suitable for agriculture and the so-called clayey Iberia in the Guadalquivir valley, center of the Douro Valley, Levantine plain and floodplain of rivers such as the Ebro and Tagus, while in areas of Iberia siliceous or limestone soils rarely found good. In the Canary Islands is even greater contrast between fertile soil on volcanic ash (Orotava Valley) and the desolation of the badlands (Lanzarote).