The mountainous islands of Brava, Santiago, Fogo, Santa Antão and São Nicolau — all with peaks over 1,000 m — are rocky, with relatively productive volcanic soils in deep valleys that support various kinds of agriculture. These islands have the longest histories of human habitation and the densest populations. The rugged landscapes consist of high peaks, ridges, plateaus and valleys. The elevations are high enough (the highest point is Mount Fogo at 2,829 m) to produce a strong orographic effect with few, but intense, precipitation events (Mannaerts and Gabriels, 2000). The mountains catch enough moisture to support grassland as well as intensive agriculture in a succession of altitudinal zones. In contrast, Maio, Boa Vista, and Sal, lying to the east, are flat, highly eroded desert islands with an arid climate marked by year-round exposure to dry winds blowing off the Sahara. Open steppe, bare soil, and long sandy beaches are the predominant land cover types. Their economy is primarily based on salt extraction and animal husbandry.