Not all the deep Andean valleys lie on or near the eastern border. Some, like the Apurimac and the Marañon, extend well into the interior of the Cordillera. Besides these deep remote valleys 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 difference 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 mineralized 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 unnecessary. 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 topographic 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 [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 below. The break between the two, a topographic unconformity, may be distinctly traced.
| Fig. 96—Snow-capped mountain, Soiroccocha, north of Arma, Cordillera Vilcapampa. The blue glacier ice descends almost to the edge of a belt of extraordinary woodland growing just under the snowline. The glacier is seen to overhang the valley and to have built on the steep valley wall terminal moraines whose outer slopes are almost precipitous. | Fig. 97—Shrubby vegetation mixed with grass at 14,000 feet (4,270 m.) on the northern or sunny slopes of the Cordillera Vilcapampa above Pampaconas, a thousand feet below the snowline. The grass is remarkably profuse and supports the flocks and herds of a pastoral population. |