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 of the drainage basin of the Rio Atacama, on the floor of which are San Pedro and adjacent towns. We were then near enough so that we could just sce the dark-green orchards of the culti- vated section of the valley; and our guide remarked, ‘Ya tenemos San Pedro en bocillo”’ (literally, Now we have San Pedro in our pocket).

The extraordinary thing about the severe cold of the Puna de Atacama is that snow so infrequently accompanies it. This is not merely an interesting physical fact of concern to the meteorologist. It is geographically important. Mid-winter snows that block the passes of the Puna de Atacama at inter- vals of several years become more frequent as we go southward towards the parallel of Copiapé, where heavy winter snows in the mountains are an annual occurrence. In a short dis- tance of several degrees we have passed from one climatic belt into another, and the effect is immediately seen upon the settlements at the base of the mountains. The Copiapé and Huasco Rivers are the first through-flowing streams of any importance whatever that we see on the map south of the Loa valley (Fig. 86). In just the region that the snows become heavier the streams take on a more permanent quality. They have excavated deep valleys that give access to the main divide, and yet the prolonged snows make the crossing of the crest of the mountains more difficult.

Though snow in some quantities falls during every winter upon the high cordillera and all the passes into Chile, it is only at intervals of a few years that the fall is heavy enough to shut off communication completely for several weeks. As a rule the cattle traffic across the mountains is not suspended because of this danger, though it introduces a source of great anxiety. In the two great storms of July 22-26 and July 30— Aug. I, 1911, about which everyone was still talking when I visited the region two years later, several herders and two parties of chinchilla hunters lost their lives, and nearly two hundred head of cattle perished also. The cattle got out of hand and strayed about at will, some to graze on the fresh