26 



II. E. Gregory — A Geologic Reconnaissance 



Mature Slopes. 



Slopes that have attained a mature stage of development 

 face Huatanay River throughout its length, constituting fea- 

 tures of large physiographic significance (figs. 5, 11, 29, 30). 



Fig. 14. 



ANGOSTURA 

 RIO HliATANAY 



CERRO-PACHATUCSA RIO-URUBAMBA 



000 



ooo 



S MILES 



Fig. 14. Profile drawn across Cuzco Valley at Angostura Narrows 

 showing mature slopes truncated at their base and leading upward to 

 plateau surfaces. < .• 



As shown on the topographic map and also in the profile 

 sections (figs. 13-18) these slopes bordering the Cuzco Valley 

 axis occupy a zone 1 to 2 miles in horizontal width whose 

 upper limit is the plateau surfaces of the Bambanusa, Huanca- 

 Huanca, and Huaca-cancha pampas, at elevations of 13,500 

 feet. Both the lower and the upper borders of the zone of 



CERRO-MUTTUY 

 l4,ooo 



2 MILES 



Fig. 15. Cross profile, Huatanay Valley, at Oropesa. 



mature slopes are marked by topographic unconformities ; at 

 about 13,500 feet mature slopes with inclinations of 1,000 to 

 1,200 feet to the mile form a contact with a surface sloping 

 about 300 feet to the mile on the Bambanusa Pampa and less 

 than 100 feet to the mile across the Huaca-cancha Pampa. 

 The topographic unconformity at the lower border of the zone 

 of mature slopes is produced by the development of canyon 



