154 THE ANDES OF SOUTHERN PERU 



into the interior of the Cordillera. Besides these deep remote val- 

 leys with their distinct climatic belts are basins, most of them with 

 outlets to the sea — broad structural depressions occurring in 

 some cases along large and in others along small drainage lines. 

 The Cuzco basin at 11,000 feet and the Abancay basin at 6,000 to 

 8,000 feet are typical. Both have abrupt borders, narrow outlets, 

 large bordering alluvial fans, and fertile irrigable soil. Their dif- 

 ference of elevation occurs at a critical level. Corn will ripen in 

 the Cuzco basin, but cane will not. Barley, wheat, and potatoes 

 are the staple crops in the one; sugar-cane, alfalfa, and fruit in 

 the other. Since both are bordered by high pastures and by min- 

 eralized rocks, the deeper Abancay basin is more varied. If it 

 were not so difficult to get its products to market by reason of its 

 inaccessibility, the Abancay basin would be the more important. 

 In both areas there is less rainfall on the basin floor than on the 

 surrounding hills and mountains, and irrigation is practised, but 

 the deeper drier basin is the more dependent upon it. Many small 

 high basins are only within the limits of potato cultivation. They 

 also receive proportionately more rain. Hence irrigation is un- 

 necessary. According as the various basins take in one or another 

 of the different product levels (Fig. 35) their life is meager and 

 unimportant or rich and interesting. 



The deep-valley type of climate has the basin factors more 

 strongly developed. Below the Canyon of Choqquequirau, a topo- 

 graphic feature comparable with the Canyon of Torontoy, the 

 Apurimac descends to 3,000 feet, broadens to several miles, and 

 has large alluvial fans built into it. Its floor is really arid, with 

 naked gravel and rock, cacti stands, and gnarled shrubs as the 

 chief elements of the landscape. Moreover the lower part of the 

 valley is the steeper. A former erosion level is indicated in Fig. 

 125. When it was in existence the slopes were more moderate than 

 now and the valley broad and open. Thereupon came uplift and 

 the incision of the stream to its present level. As a result, a steep 

 canyon was cut in the floor of a mature valley. Hence the slopes 

 are in a relation unlike that of most of the slopes in our most 

 familiar landscapes. The gentle slopes are above, the steep be- 



