126 ; SIERRA DE UMANGO 
per mile. Further the quoted author states: , The sheetflood is 
characterized by a tendency to spread widely in relatively narrow 
sheets (of gravel loaded water). In a general way, streams prevail 
in humid regions, sheet floods in arid regions, though streams occur 
locally also in arid lands, while it seems probable, that sheet floods | 
occur under certain conditions in nearly all lands, howsoever humid.“ — 
Almost all the above enumerated conditions prevail in the Sierra 
de Umango area, and the sheet flood phenomenon has therefore 
Fig. 22. High destructive, diluvial (?) terraces, carved out in red sandstones. Southeastern side of 
the Nevado de Famatina at Puerto Alegre. Looking north. The high ridges in the background are 
granite. The ranch lies on a subrecent sheetflood surface. 
here a very typical development. Rapid precipitations occur in 
summertime in the form of the so called ,crecientes«. The soil is 
in the shallowest underground already quite hard, consisting of the 
endurated continental sandstones. 
The same conditions for sheet flooding have prevailed down to 
quite recent times during the successive degradation of the sand- 
stone mantle oi the crystalline block sides. The whole process was 
merely a formation of lower and lower, gentle sloping terrace pla- 
nes, a kind of destructive terraces, carved out in the sandstone mass. 
Very few older sheet flood terraces (situated on higher levels) 
are yet visible. In the ,intermontane zone“ there are in some parts 
