PHYSICAL GEOGRAPHY 723 



ing hills which at many places parallel this range are of considerable 

 prominence in the vicinity of Tareiri, where they coalesce into a ridge 

 200 feet in height, paralleling the sierra for many miles and passing just 

 east of the village. 



Farther south, near Yacuiva, there is a group of rather prominent hills, 

 known as the Cuestas de Ipahuazo, situated 8 to 12 miles east of the 

 Sierra de Aguarague. These hills are heavily wooded and among them 

 there are few exposures of underlying rocks. The generally softened, 

 rolling topography offers many suggestions of alignment parallel to the 

 trend (north 20 degrees east) of the neighboring sierra. The western 

 margin of these hills is sharply denned by dip slopes, 150 to 300 feet 

 high, which rise from the broad shallow valley traversed by the trail from 

 Palmar, past Yacuiva, to Aguaray. The hills are doubtless a response to 

 the deformation of the resistant sandstones and may be structurally the 

 continuation of the Sierra de Charagua, although topographically they 

 are far removed from that mountain range. 



INTERMONTANE LOWLANDS 



Between the northward-trending mountain ranges above described, 

 there are intermontane depressions, 3 to 15 miles in width, which stretch 

 for long distances north and south. These lowlands display in general an 

 undulating topography with moderate relief. With the exception of the 

 prominent cuestas which occupy certain of these depressions, the eleva- 

 tions on them are quite irregular in distribution and have soft, rounded 

 outlines, in striking contrast to the sharp profiles of the adjacent sierras. 

 South of Cangapi, where the streamlets which drain these intermontane 

 depressions are tributary to Rio Vitiacua, the topography is much more 

 broken than in the north part of the area under discussion. Because of 

 the lower baselevel of Eio Vitiacua and the other tributaries to the Pilco- 

 mayo, the interstream areas there are carved into fairly sharp ridges sepa- 

 rated by youthful ravines, suggesting greater erosional efficiency od the 

 part of the Pilcomayo and its tributaries than that displayed by the afflu- 

 ents of Rio Grande. 



The intermontane depression west of the Sierra de Charagua is modi- 

 fied by two lines of prominent hills. The eastern group forms the Cuestas 

 de Oquita, the northern extension of which is locally referred to as the 

 Cuestas de Taimbermi. These hills are separated from the Sierra de 

 Charagua on the east by a long, narrow lowland about 3 miles in width, 

 drained by various tributaries to Rios Saipuru, Charagua, and Parapiti. 

 Their east margin is a bold, rugged cliff which extends for at least 40 

 miles from a point far to the north of Taimbermi southward bevond Rio 



