of the Cuzco Valley, Peru. 



51 



channels ; on a few of them the work is complete. The fans 

 are trenched with canyons which compare in depth with adjoin- 

 ing rock-walled gorges. Above Cuzco the Huatanay (Zappi) 

 has again reached bedrock and the entire Cuzco fan is dis- 

 sected by straight-sided, gravel-walled trenches 100 to 200 feet 

 in depth (figs. 5, 13, 21). A section of the San Geronimo 



Fig. 32. 



Fig. 32. Terraces along the Huatanay, at Condor-Koma, cut in ancient 

 lacustrine deposits. 



fan reveals the presence of a series of narrow, flat-bottomed, 

 vertical-walled gravel canyons intrenched to a depth of 100 

 feet, without, however, reaching strata of preglacial age. Like- 

 wise the tilted lake beds adjoining the village of San Sebastian 

 are deeply trenched (fig. 31). At Angostura Narrows bedrock 

 has been exposed by the removal of about 600 feet of gravel 

 (fig. 20), and along the south side of the Cuzco Basin dissection 

 of piedmont gravels and lake sediments is unusuallv conspicuous 

 (fig. 29). 



Terraces. — That postglacial erosion has not continued at a 

 uniform rate but has been subject to marked fluctuation and 

 interrupted by periods of aggradation is indicated by a wide- 

 spread development of terraces. Along the upper Huatanay 



