Some 80km north of Valle Fértil, the PARQUE PROVINCIAL ISCHIGUALASTO, also known as the Valle de la Luna, or Moon Valley, is San Juan’s most famous feature by far, covering nearly 150 square kilometres of desolate but astonishingly varied terrain.

For paleontologists, Ischigualasto’s importance is primarily as a rich dinosaur burial ground: two of the world’s very oldest species of dinosaur, the diminutive Euraptor lunesis and Herrerasaurus ischigualastensis, both dating back some 230 million years, were found here, among many others. The park is also a joy for geologists, as most strata of the 45-million-year Triassic era are on plain view.

The park is in a desert valley between two ranges of high mountains, the Sierra Los Rastros to the west and Cerros Colorados to the east. As witnessed by the mollusc and coral fossils found in the cliffsides, for a long time the whole area was under water. Over the course of millions of years the terrain has been eroded by wind and water, and sections built of volcanic ash have taken on a ghostly greyish-white hue. A set of red-sandstone mountains to the north acts as a perfect backdrop to the paler stone formations and clay blocks, all of which are impressively illuminated in the late evening.

At the entrance, an excellent museum exhibits some wonderful stories of forensic paleontology, unravelling some curious examples of dinosaur death (Spanish only) – useful while you wait for a tour.

The majority of visitors come to admire the spectacular lunar landscapes that give the park its popular nickname, and the much publicized and alarmingly fragile rock formations – some have already disappeared, the victims of erosion and the occasional flash floods that seem to strike with increasing frequency. Cerro El Morado (1700m), a barrow-like mountain that according to local lore is shaped like an Indian lying on his back, dominates the park to the east. A segmented row of rocks is known as El Gusano (the Worm); a huge set of vessel-like boulders is known as El Submarino; a sandy field dotted with cannon-ball-shaped stones is dubbed the Cancha de Bolas (the Ball-court). One famous formation, painfully fragile on its slender stalk, is El Hongo (the Mushroom), beautifully set off against the red sandstone cliffs behind.

Another of the park’s attractions is its wealth of flora and fauna. The main plant varieties are the native broom-like brea, three varieties of the scrawny jarilla, both black and white species of algarrobo, the chañarretamo and molle shrubs and four varieties of cactus. Animals that you are likely to spot here include European hares, Patagonian hares, the vizcacha, the grey fox, armadillos and small rodents, plus several species of bat, frog, toad, lizard and snake. Condors and ñandús are often seen, too, while guanacos may be spotted standing like sentinels atop the rocks, before scampering off.

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