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 has gathered chemical elements from the adjacent lava slopes which they drain.

In consequence of the greater precipitation and larger streams on the castern border of the Puna a vastly greater amount of erosion has taken place there than on the western border of the Puna. In contrast to the feeble Copiapé River, which reaches the sea only at long intervals in latitude 27° 20′,

. 88—Schematic diagram of the Puna and its eastern border to represent enclosed basins on the western side of and among volcanic ranges and through-flowing drainage east of them.

are the headwaters of the Colorado (or Bermejo) River in the Fiambala district and in the Chaschuil district, where inter- mittent streams from at least three principal mountain masses furnish water for a widely ramifying system of tributaries.

Viewed from the trail on the Cuesta del Obispo (Fig. 63, p. 203) the eastern rampart of the Puna has a distinctly mountainous appearance; seen from the west it forms a some- what tame landscape. The border chain has high passes and relatively low peaks. The passes run from 5000 meters to 5400 meters (16,500 to 17,500 feet), but the peaks are only a little higher; that is to say, they range in elevation from 5500 to 6000 meters (18,000 to 20,000 feet). The passes have been but little eroded, for the mountain border is in a state of extreme youth. By contrast the Cordillera de los Andes, or Maritime Cordillera, which borders the Puna de Atacama on the west, averages about 4600 meters (15,000 feet), but the peaks run up to 6000 meters (20,000 feet) or 7000 meters (23,000 feet). The cones on the eastern side of the Puna are