Page:Isaiah Bowman - Desert Trails of Atacama (1924).pdf/284

 in the widely extended valleys that unite to form the head- waters of the Rio Salado between Tucuman and Salta reflect the slightly moister climate and more nearly normal drainage that characterize the eastern border of the Puna,

The western mountain divide of the Puna is formed by the Cordillera de los Andes, which consists chiefly of a line of high volcanoes with lava flows about them. The highest elevations run between 18,000 and 20,000 feet. Upon the mountains the summer winds are from the east, the winter winds from the west, so that from December to March, as in the Copiapé region, there is a period of melting snows, and from June to August there is a period when the moist winds from the Pacific increase the snow fields and sometimes lay an extensive cover of snow over the whole of the mountain belt. The Copiapé valley receives part of the run-off from melting snow in the high volcanoes, and its flow is thereby made regular enough to support farming in the Copiap6é valley—which gives a critical geographical value to this part of the Andean Cordillera of South America, in the study of human distributions.

West of the Cordillera de los Andes and for 3000 to 4000 feet below the Puna level, or at 7000 to 8000 feet above the sea, there is a line of depressions which includes the great Salar de Atacama and the Salar de Punta Negra. These are enclosed on their western side by the Cordillera Domeyko (Fig. 87). The region is considered as a portion of the Desert of Ata- cama, because in its irrigated sections are produced fruit, grain, and forage in abundance in contrast to the cold, deso- late, and largely uninhabitable character of the high Puna country (sce Chapter X11). It is quite a different world, and after the mountains it seems extremely hospitable.

The quality of the relief and drainage on the western border of the Cordillera de los Andes and about the basin borders in the Desert of Atacama is shown in Figure 93, which is a reduc- tion from a contour map made by the Peñon Syndicate. The map is especially valuable because so small a part of the Desert of Atacama has been accurately mapped. The