12 II. E. Gregory — A Geologic Reconnaissance 



Huatanay 4 occupies a channel lined by walls of ancient design 

 which lead the stream to the south side of the valley. In this 

 part of its course the water level is maintained by a dam which 

 controls the location of irrigation ditches. From its junction 

 with the Huancaro to a point below San Sebastian the Huat- 

 anay is constrained to follow the rim of the Cuzco Basin, thus 

 reclaiming lands otherwise subject to flooding. Below the 



Fig. G. 



Fig. 6. The village of San Geronimo at the lower end of the Cuzco 

 Basin showing its position on the margin of an alluvial fan. 



mouth of Rio Huilcarpay the stream returns to the center of 

 the valley, following a natural course around the low divide 

 separating the two portions of the Cuzco Basin, and encircling 

 the foot of San Geronimo fan until confined hj the walls of 

 the Angostura Narrows. Below Angostura the Huatanay, 

 except where artificially controlled, is a sluggish, meandering 

 stream. For an S-mile stretch below Saylla, across the flat 

 floors of the Oropesa and Lucre basins (fig. 7), the total fall 

 of the stream is only 160 feet. The quality of the profile of 

 the Huatanay is shown in fig. 8. 



Tributaries to the Huatanay vary greatly in amount and 

 permanency of flow. Above Cuzco the streams are moderately 

 4 Locally called Rio Zappi. 



