The plains are covered by a formation similar to that of the Argentine pampas and by the alluvial deposits of the present rivers.
==Geology== The Pampas of Argentina are generally covered by loess.
Evidence of this is to be found in the altitudes of the stations on the Buenos Aires and Pacific railway running a little north of west across the pampas to Mendoza.
The flora of Argentina should be studied according to natural zones corresponding to the physical divisions of the country - the rich tropical and sub-tropical regions of the north, the treeless pampas of the centre, the desert steppes of the south, and the arid plateaus of the north-west.
Paspalum, is a large tropical genus, most abundant in America, especially on the pampas and campos; many species are good forage plants, and the grain is sometimes used for food.