|Limite to the North with the region of the Northwest, to the This with the mountains Pampeanas and the plain pampeana, to the South with the Andean Patagonia and extrandina and to the West with the republic of Chile. They can be distinguished three subregiones: 1) the mountainous area, subdivided in Mountain range of the Andes and Precordiliera of The Rioja, San Juan and Mendoza; 2) the watering oasis and 3) the plains of the Easts.
The difference between the Mountain range and the Precordillera is fundamentally geologic: the Andes of the geosinclinal is the element more modern orogénico, being an old marine, narrow and lengthened basin whose silts were folded and lifted until the biggest heights during the Cenozoico, with accompaniment of magmatic gushes. The Precordiliera is composed by silts paleozoicos folded in that era and lifted then by the Andean orogeny; toward the This is separated from the Mountains Pampeanas for a fracture line characterized by an intense seismic activity.
The Arid Andes or Power stations present two cords: the Westerner, for which the Argentinean-Chilean limit runs, is almost continuous presenting steps of great height, it takes the dividing of waters being born in them mighty rivers that run for valleys straits fields of brashes. From Mendoza's South and until approximately the 37° S, is prolonged in the Andes of Transition that present more snow in the summits and bigger vegetation when varying the climatic conditions.
The oriental cord, call also Front mountain range, is presented in form discontínua to be cut by the traverse valleys of the rivers that lower from the West; in him they are the highest summits (Aconcagua, Tupungato, etc). A series of valleys straits locally denominated drawers, they separate both cords, characterized by their great aridity.
Among the hills Aconcagua and Tupungato the aspect of the mountain range begins to change, extensive glaciers appear and more to the South volcanos (Overo, Peteroa), accompanied by big extensions covered with scums and mantels of lava.
To the East of the arid Andes they are located a series of wide longitudinal valleys (Rodeo, iglesia, Barreal and other) in those that thick materials coming from the mechanical disintegration of the rocks cordilleranas prevail, but that they possess their snub funds covered with very fine materials.
The Valley of Barreal is a basin without deagüe whose bottom is occupied by the barreal of the Leoncito, while the valley of Uspallata is crossed by the South by the river Mendoza. They are a series of watering oasis here, among those that Calingasta and Uspallata stand out; these valleys separate to the Andean mountain range of the Precordillera. whose summits lack of persistent snow.
A reduced number of rivers crosses the Precordiliera for narrow valleys, at the end of which form extensive cones of connected deyección with the plains. This fine material has served from seat to important cultivation oasis, in the North section he/she stands out that of Jáchal and more to the South the main of the area: that of San Juan and that of Mendoza, prolonged in that of the Tunuyán. The rivers that travel these oasis have been taken advantage of for the energy production and the obtaining of water for watering, standing out the reservoir of Ullún.
The southern courses (Diamante and Atuel) they have generated oasis of watering that have as outstanding urban centers to San Rafael and General Alvear. In the river Atuel, the topographical characteristics allowed to build the reservoir of the Nihuil whose important energy production justifies the radicación in the area of heavy industries.
The surface of the oasis is dedicated to the vine cultivation, olive tree, fruit-bearing and vegetables. Also you siembra medic to feed to the bovine livestock, and some cereals but in reduced extensions. Although in small scale the extensive cattle raising is developed with certain trashumancia forms, taking to pasture the livestock in summer to the mountainous area.
The mining is also very important, standing out the petroleum especially in Tupungato, being also exploited copper (El Pachón in San Juan), uranium, lead, zinc, calcareous and marbles.
Toward the East they expand the plains of arcillo-sandy floors, of great aridity and reduced slope. The scarce rains torrential erosionan deep gutters that still disable the displacement with horses, conforming those denominated "huayquerías" or voyages, as those of the Tunuyán.