122 SIERRA DE UMANGO 
Rio Bermejo, which follows in its upper part the Guandacol valley 
and runs then southward along the western border of the Sierra de 
la Huerta between this mountain and the Sierra Pié de Palo. Fur- 
ther to the south the river joins the Rio Desagiiadero. Here the 
plain lies 457 m over the sea. The last named river flows then 
further southward, ending in a wide depression without outflow, in 
the Gobernaciön de La Pampa. 
At present time the Sierra de Umango has consequently no drai- 
nage to the sea, in this respect being of the same nature as the 
whole interior part of the Republic between Tucumän in the north 
and the headwaters of the Rio Colorado in the south. 
The more distant bases of erosion are, however, of no importance 
for the development of the land-sculpture in the Umango area. Here 
may only be considered the local bases, each of these being in arid 
conditions and of great influence upon the forming of the sculpture. 
The lowermost local baselevel of the Umango area is represen- 
ted by the bottom of the Guandacol valley. Other somewhat hig- 
her levels are the Pagancillo and the Jaguel bolson floors. The 
absolute heights of the different plains are as follows: 
Valley of Girandacols:. Yes, 910—950 m. 
Pasancillo lowland N... ee 1190 m. 
Valleyeok Vinchina oi. mer 1260 —1400 m. 
JA SUSAN OLSON So sen Nee 1844 m. 
VaileyeotePambillos so nase. 2225 m. 
At present the erosion is controlled by an arid climate,! which 
seems to have prevailed during the whole quaternary and recent 
periods. The development of the landsculpture in desert regions 
has been explained by W. M. Davis.” According to W. M. Da- 
vis, the enumerated local erosion bases cause a corresponding 
1G. Davis; El clima de la Repüblica Argentina. Buenos Aires 1909. Page 73. 
2 W. M. Davis: The geographical cycle in an arid climate. The Journal of 
Geology. July-Aug. 1915. 
PES USB BR. 
