The Colorado and Barrancas rivers, which run from the Andes to the Atlantic, are commonly considered the northern limit of Argentine Patagonia. The archipelago of Tierra del Fuego is sometimes included as part of Patagonia. Most geographers and historians locate the northern limit of Chilean Patagonia at Reloncaví Estuary.
The name Patagonia comes from the word patagón, which was used by Magellan in 1520 to describe the native tribes of the region, whom his expedition thought to be giants. It is now believed that the people he called the Patagons were Tehuelches, who tended to be taller than Europeans of the time.
The Argentine researcher Miguel Doura observed that the name Patagonia possibly derives from the ancient Greek region of modern Turkey called Paflagonia, possible home of the patagon personage in the chivalric romances Primaleon printed in 1512, ten years before Magellan arrived in these southern lands. The hypothesis was accepted and published in a 2011 New Review of Spanish Philology report.
Argentine Patagonia is for the most part a region of steppelike plains, rising in a succession of 13 abrupt terraces about 100 metres (330 feet) at a time, and covered with an enormous bed of shingle almost bare of vegetation. In the hollows of the plains are ponds or lakes of fresh and brackish water. Towards Chilean territory the shingle gives place to porphyry, granite, and basalt lavas, animal life becomes more abundant and vegetation more luxuriant, consisting principally of southern beech and conifers. The high rainfall against the western Andes (Wet Andes) and the low sea surface temperatures offshore give rise to cold and humid air masses, contributing to the ice-fields and glaciers, the largest ice-fields in the Southern hemisphere outside of Antarctica.