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. 66—The upper Calchaquí valley. Campo Negro is a volcanic flow that blocked the valley making a lake in the Poma district. When the outlet was cut down the lake bottom became a valley floor, The other shaded areas represent irrigated districts.

crop. It decorates the valley and makes it seem exceptionally attractive after one has journeyed over the lava flows and coarse piedmont of the intervening ba- sins and mountains. So fertile is the soil of the Calchaqui val- ley at Poma that al- falfa lasts for twen- ty-five years without resowing, whereas at Salta and Santa Fé it lasts but three years on account of the heat and drought. This means much less work in the higher valleys and a corresponding economy in the man- agement of an estate. Yet the climate is sufficiently mild in winter to permit open grazing. The fields aretherefore pastured the whole year round, and the grass is not cut for hay except for limited winter feed- ing: The work on a given ranch, or finca, as on that of La Poma, is chiefly to open ditches and clean them out each