The Patagonian Desert, also called the Patagonian Steppe, is a cold desert of about 673,000 km² (260,000 sq mi) covering most of southern Argentina, with smaller areas in Chile, between the Andes to the west and the Atlantic Ocean to the east. It is the largest desert in Argentina and about the eighth-largest in the world. Rather than sand dunes, it is a land of stepped tablelands, basalt plateaus and gravel plains cut by river canyons, covered in tussock grass and low shrubs and swept by near-constant westerly winds. It exists because the Andes, rising since the Middle Miocene about 14 to 12 million years ago, block moist Pacific air, leaving a rain shadow that the cold Falkland Current offshore makes even drier. A 2017 assessment found about 12 percent of the ecoregion, 70,970 km², inside protected areas, among them Los Glaciares, Bosques Petrificados de Jaramillo and the Valdés Biosphere Reserve. This guide travels it from its northern edge to the Strait of Magellan, crossing one river valley after another.
Río Colorado: the northern threshold
The journey starts on the Colorado River, commonly taken as the northern limit of Argentine Patagonia. Rising on the eastern slopes of the Andes at about 34°48' S, it runs east-south-east for about 1,000 km, marking most of the boundary between the provinces of Neuquén and Mendoza and then between Río Negro and La Pampa, before ending in a delta 100 to 120 km south of Bahía Blanca. North of it, the steppe grades into the Monte scrubland and the Cuyo region. Its banks are fertile and wooded, but the strip is too narrow to carry more than a scattered population, and the land on either side is already dry. In summer this northern fringe is the warmest part of the desert, with days reaching about 31 °C.
Río Negro and the orchards of the Alto Valle
Next comes the Río Negro, Patagonia's largest river by drainage basin. It forms where the Limay and Neuquén rivers meet on the Neuquén border, with the Alto Valle cities of Cipolletti and General Roca near its head, and runs 635 km to the Atlantic near El Cóndor, about 30 km below the provincial capital Viedma. Its Mapuche name, Curu Leuvu, means "black river", although the water is greener than black. The valley is a ribbon of irrigated green: Río Negro province grows about 70 percent of Argentina's pears and 72 percent of its apples, and about 48 percent of the Southern Hemisphere's pears. Lamarque, on Choele Choel Island in the middle valley, calls itself the national capital of the tomato.
The river also marks a violent chapter. During the Argentine army's Conquest of the Desert in the late 1870s and early 1880s, it briefly served as the line between the state and Indigenous territory. Before then, Tehuelche hunter-gatherers had roamed the steppe, and from the 18th century the Mapuche, who kept horses, came to control trade across it as far as Buenos Aires and southern Chile. Argentine troops killed more than 1,000 Indigenous people, took an estimated 10,000 prisoner and drove many thousands more from their lands. A boundary treaty with Chile in 1881 then placed most of the desert under Argentine sovereignty.
Over the Somún Curá basalt tableland
South of the Río Negro the road climbs onto the North Patagonian Massif, also called the Somún Curá Massif, a plateau of about 100,000 km² that stands 500 to 700 m above the surrounding land and reaches 1,200 m above sea level. Much of its surface is volcanic rock. Volcanic rock covers more than 120,000 km² of the Patagonian Desert, mostly here and in the Deseado Massif further south, the product of back-arc volcanism behind the Andes in two main episodes: one in the Eocene and Miocene and another from the late Miocene to the Pleistocene.
Winters are long and frosts common, though snow is rare because the air is so dry. The northern inland plateaus range from about −5 °C to 5 °C in winter, and the official cold record is −33.9 °C, set in Chubut province. The westerly wind barely stops, and it lifts so much fine material that Patagonia is one of the largest sources of dust over the South Atlantic. Guanacos, lesser rheas, maras, Patagonian grey foxes and pumas live on the steppe, while tufted grasses such as Stipa and Poa replace shrubs toward the wetter west. For why a desert can be this cold, see our explainer on the cold desert climate.
Puerto Madryn, Península Valdés and the Welsh Chubut valley
The road drops to the Atlantic at Golfo Nuevo. On 28 July 1865, 153 Welsh settlers landed here from the clipper Mimosa. They had been promised country like lowland Wales and found an arid plain with little drinking water. The town at their landing place is now Puerto Madryn. Across the gulf lies Península Valdés, about 3,625 km² of barren land with salt lakes, the largest about 40 m below sea level. It became a UNESCO World Heritage Site in 1999 for its marine life: the gulfs on either side are the world's most important breeding ground for southern right whales, which arrive between May and December, and the coast with neighbouring Punta León and Punta Loma supports about 150,000 breeding pairs of Magellanic penguins.
From Madryn it was about 40 miles over the thorn desert to the Chubut River, where the settlers built their first fort on the site of today's Rawson. Its name comes from the Tehuelche word chupat, "transparent", while the Welsh called it Afon Camwy, the "twisting river". It flows about 800 km from the Andean foothills between Bariloche and Esquel to Engaño Bay near Rawson, carrying anything from 4 to 400 m³ a second. After a disastrous harvest in 1881, the colonists dug an irrigation system from 1882 under the engineer E. J. Williams, and wheat from the valley became a mainstay of Patagonian farming. Trelew, named after the settler leader Lewis Jones, grew at the head of the railway to Madryn begun in 1886. Today the Welsh-Argentine community centres on Gaiman, Dolavon, Trelew and Trevelin, with an estimated 1,500 to 5,000 Welsh speakers. Some 120 to 140 km west of Trelew, the Florentino Ameghino Dam, inaugurated in 1963, holds back a 70 km² reservoir and powers towns as far south as Comodoro Rivadavia.
Comodoro Rivadavia and the San Jorge Gulf oilfield
Further south along the coast, Comodoro Rivadavia sits at the foot of Chenque Hill on the San Jorge Gulf. Founded by decree on 23 February 1901 as a port for the inland settlement of Sarmiento, it changed in 1907, when a crew drilling for water struck oil at 539 m. It is now the largest city in Chubut and the largest south of the 45th parallel, with 182,631 people in the 2010 census, and a 1,770 km pipeline carries its natural gas to Buenos Aires. Oil, gas and coal remain, with sheep and goat farming, the main ways the desert earns a living. In the decades either side of 1900 the less arid steppe went through a sheep-farming boom that made the region one of the world's great exporters of sheep products.
Up the Deseado: petrified forest and the Pinturas canyon
The Deseado River, named after John Davis's ship Desire of the 1592 Cavendish expedition, runs 615 km south-east to Puerto Deseado. It is a fragile river: it sometimes vanishes beneath the arid ground before re-emerging near the coast, where its drowned mouth has been the Ría Deseado nature reserve since 1977.
Inland, in Santa Cruz's Deseado Department, the desert holds a record of a wetter past. In the Late Jurassic, about 150 million years ago, dense forests of giant conifers such as Araucaria mirabilis grew here. At the start of the Cretaceous, volcanic eruptions buried them in ash, and mineral-rich water turned the wood to stone. The trunks, found in 1925, now lie on the surface of Jaramillo Petrified Forest National Park, some 2 m across and others 30 m long. Protected as a natural monument from 1954, the site became a national park of 78,543 hectares in December 2012.
The same massif is ancient underneath. Its mantle roots are 2,100 to 1,000 million years old, making it one of the oldest parts of Patagonia, and it hosts epithermal gold mines such as Cerro Vanguardia and Manantial Espejo. Upstream on the Deseado's tributary, the Pinturas River has cut a stepped canyon into the plateau. At the base of one cliff is Cueva de las Manos, 163 km south of the town of Perito Moreno, where hundreds of hand stencils were sprayed on the rock in several waves between about 7,300 BC and AD 700. Systematic research began in 1964 under the archaeologist Carlos J. Gradin, and the site is now a UNESCO World Heritage Site.
From San Julián's depression to Pali-Aike and the Strait of Magellan
Back on the coast, the steppe hides the lowest ground in the Americas. Laguna del Carbón, a salt lake in the Gran Bajo de San Julián about 54 km from Puerto San Julián, lies 105 m below sea level, the seventh-lowest point on Earth.
Further south comes the Santa Cruz River, which drains Lakes Viedma and Argentino in Los Glaciares National Park and runs 385 km east to the Atlantic with an average flow of 790 m³ a second, one of the last large free-flowing rivers in Patagonia. Juan Serrano, captain of Magellan's ship Santiago, reached its mouth by 5 August 1520. In April 1834 Robert FitzRoy and Charles Darwin of HMS Beagle led 25 men upriver, hauling boats for 16 days across the plateau. Two dams, Jorge Cepernic and Néstor Kirchner, with a combined planned capacity of 1,740 MW, were contracted in 2013. Our guide to the glaciers of Patagonia follows the river back to the ice that feeds it.
The last stretch crosses the Pali-Aike volcanic field on the Argentina–Chile border, about 467 vents spread over 4,500 km², active from 3.78 million years ago into the Holocene. Its name is Tehuelche: pale, "hunger", and aike, "place". Río Gallegos lies within 23 km of it, and archaeological sites such as Fell Cave show people living here for thousands of years. Beyond the field, the steppe meets the Strait of Magellan, and the same wind-scoured grassland continues across the water onto the northern plains of Tierra del Fuego.