4S 



H. E. Gregory — A Geologic Reconnaissance 



and physiographic history of this fan have been fully described 

 in a previous paper. 21 



The San Geronimo fan is formed of enormous quantities of 

 land waste washed from the slopes of Cerro Picol and deposited 

 on the floor of the Cuzco Basin. The alluvial sediments thus 

 supplied extend nearly across the Cuzco Valley and are respon- 

 sible for the existence of the agricultural community centered 



Fig. 30. 









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. 



u 





ms 



^WF% 





"-- 



































... H| 











slSSi 



^g~.^ 





















ggg 







" "". 1 



Spi 

















B8JB->i55 













' c 







' 









n £' Si 



w^-*p 



























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Fig. 30. The San Geronimo fan extending south, from the hase of Cerro 

 Picol. A. H. Bunistead, photo. 



at San Geronimo. Measured along Huatanay River the foot 

 of the San Geronimo fan is 4 miles long; its width from the 

 base of the rock slopes southward to its periphery is a little 

 less than 11/2 miles. Its surface slopes about 450 feet in a 

 mile. As seen in the photograph (fig. 30), the fan has received 

 its gravels from the streams traversing the steep middle slopes 

 of Cerro Picol — streams which head in cirques and glaciated 

 valleys leading from pyramidal summits. From the crest of 

 the mountain (14,607 feet) to the head of the fan (11,500 

 feet) these streams descend at the rate of about 1,600 feet to 

 the mile. At the present time the mountain slopes are almost 

 bare, and little material is carried by the swiftly flowing 

 brooks. In fact, the streams traversing the fan are now 

 intrenching themselves near the mountain base, and their work 



21 Gregory, The gravels at Cuzco, Peru, this Journal, xxxvi, pp. 15-29, 

 1912. 



