The subhumid grasslands of South America, also known as the Rio de la Plata grasslands, extend over 700,000 km2 (270,272 mi2) and are divided into two sub-regions: the pampas and the campos. These grasslands are dominantly comprised of mesothermic grass species with a mild climate characterized by mean annual temperatures of between 10 to 20 ° C (50 to 68 °F) and rainfall between 400 and 1600 mm (16 and 63 in)(1). The pampas occur in the Buenos Aires province of Argentina and in parts of the provinces Entre Rios, Santa Fe, Cordoba, La Pampa and San Luis. Active urbanization and agricultural expansion have made the pampas the most impacted ecoregion of Argentina. General species composition of the area includes Stipa, Piptochaetium, Aristida, Melica, Briza, Bromus, Eragrostis and Poa. Soil classification in the area ranges from vertisols (high clay content) to entisols (sandy, deposited soils) with varying degrees of surface litter. The campos have a relatively flat, low elevation (reaching at a maximum 700 m (2297 ft) above sea level) and occupy portions of Uruguay and the southern Rio Grande do Sul province of Brazil. Soils in this region are generally comprised of loess deposits overlaying a crystalline basement (such as slate or igneous rock), but the dominant geologic materials are far more diverse than those of the pampas.