24 



H. E. Gregory — A Geologic Reconnaissance 



Plateaus. 



In the Cuzco region the widespread Inca peneplain has been 

 trenched by the Urnbamba to a depth exceeding 5,000 feet 

 and by the Huatanay to an average depth of 3,000 feet below 

 the ancient base-leveled surface. On the southern upland bor- 

 der of the Cuzco Valley a remnant of the Inca peneplain is 

 preserved at an elevation of 13,500 feet over an extent of 



Fig. 12. 



Fig. 12. Surface of Puquin Plateau, elevation 13,200-13,600 feet, show- 

 ing geologic structure and character of dissection. Isaiah Bowman, photo. 



about 30 square miles (fig. 11). The portion of this area 

 known as Pampa de Huaca-cancha is a local plateau whose 

 surface is made up of a group of low, oblong domes separated 

 by wide, flat-floored valleys. Westward from Huaca-cancha 

 upturned beds of alternating resistant conglomerate and weak 

 shales have permitted intricate erosion, without, however, 

 destroying the plateau form (fig. 12). North of the Cuzco 

 Valley axis the Inca peneplain is represented by the Bambanusa 

 and Huanca-Huanca pampas, whose average elevation is 

 13,500 feet. The surface of these pampas has been consider- 



