2 SIERRA DE UMANGO 
lowland ridges, built up by soft, younger rocks, principally of 
clastic origin. Of the lofty „erystalline“ mountains, the Cerro Cacho 
lies nearest to the Cordilleran border and is for a distance of some 
miles closely united with the later (Pampa de Leoncito). Separated ; 
N 
; 
a 
from the Cerro Cacho by a relatively hilly highland surface there © 
follows to the east the very ridge of the Sierra de Umango, run- | 
ning NE--SW, with a somewhat lower and shorter parallel chain : 
to the east, the Cerro La Pampa. To the SE off these ridges lies i 
the more isolated complex of the Cerro Villa Union, on all sides © 
surrounded by alluvial deposits. 
All the named mountains are of quite considerable heights, as - 
shown by the following data: 
Gerro(Gachoerwas oe Fae 4,660—4,405 m ab. the sea. 
Sierra de Umango ridge ... 4,300—4,275 , , , 5 
Cerro Villa Union. 8.2... ISDN RN x 
The absolute heights of the valleys vary between 910 and 2,200 — 
m. The foothills and the lowland ridges of softer rocks and also © 
isolated groups of the old basement rocks (Villa Castelli) attain only 
some hundred meters over the valley floors. Of greater importance 
among the foothills are the Cerros de San Antonio to the S from 
the Sierra de Umango ridge, the Cerro Bola SSE from the Cerro 
Villa Union, the Cerro Colorado, lying immediately to the east of 
the Cerro Villa Union and at last the broad ridge, well marked by — 
a cuesta to the E, forming the dividing line between the Jaguel - 
bolson and the Vinchina valley in the direction NE from the Sierra 
de Umango. (See the topographical map!) 
The whole western part of the province of La Rioja belongs to 
the climatic province of broader sense called by G. Davis! ,Za zona 
andina“. This is, as known, characterized as a dry desert, where 
rainfall occasionally occurs only in summertime, when the Eastwind 
blows (from the pampa). In the higher mountains a western storm 
1 El clima de la Republica Argentina. Buenos Aires. 1909. 
