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 intervals it may be that a large through-flowing stream may collect the drainage of a string of basins and minor valleys. If the rainfall increases in amount there is a corresponding in-

. 18—Interior-basin types of drainage features upon the high and cokl Puna de Atacama and other arid or semi-arid plateau-and-mountain regions adjacent. Short disconnected drainage systems are the rule, with intermittent streams and salt-covered basin floors. See Fig. 1, p. to, for the general geographical setting.

crease of stream organization. The individual basins are no longer isolated and self-contained but receive the water and waste of tributary streams upon their floors, while the self- contained basin has a salt lake or a salt-incrusted floor with wide marginal flats. In the season of rain the floors of the con- nected basins are generally drained by incised streams that are rapidly cutting their way downward in the general process