Pedroseños fundadores de Buenos Aires Curiosity · El Pedroso, Sierra Norte, Seville Image of El Pedroso, not of the place itself. In 1535 Pedro de Mendoza's expedition to the Río de la Plata set out with five colonists native to El Pedroso, who took part in the founding of Buenos Aires and Asunción. 1535 Photo: kallerna (CC BY-SA 4.0) What to see and do in El Pedroso