The Triassic Basin of Ischigualasto or “the Valley of the Moon”, as it is called by geologists and paleontologists-is a vast depression characterized by the proliferation of a series of ancient sediments, belonging to the Triassic geological period, which lasted some 45 million years before the beginning of the Mesozoic era.
The land, which until then was only inhabited by plants and insects, began to be invaded by reptiles, which flourished and reproduced freely, without any competition.
The climate of this region then was a wet, tropical one where vegetation must have been extremely lush and abundant. Neither the Andes Mountains nor the Famatina Mountain range, which can be seen from various points in the valley, had been formed.
Instead, there were lagoons and swamps, whose vegetation transformed into carbon deposits, which can be seen in the South of the valley, where the oldest of the three series of sediments, known as “Los Rastros” formation lies, with its distinctively greenish, brownish, and blackish rocks.
“The Submarine” and “the Worm” are peculiar rock formations, sculpted by the constant action of wind erosion over these sedimentary rocks. Slowly, so very slowly, over a period of millions of years, the climate and the landscape mutated. Rainfall diminished, draining the region. Wind eroded the rocks and deposited new sediments over previous formations.
The flora and fauna likewise underwent mutations. The first seed-plants appeared as well as a wide variety of medium-sized reptiles, like the Cynodonts or Dicynodonts, two types of herbivores, and the Saurosuchus, one of the carnivores.

The Ischigualasto Formation, which forms the central part of the valley, belongs to this period. Some of these grey-green rocks were eroded into strange formations, which today are known as “Alladin’s Lamp”, “the Parrot “, “the Mushroom”, and “the Painted Valley”.
The meteorological alterations continued. By the conclusion of the Triassic Period, this rift valley was a windswept desert inhabited by even larger, more advanced reptiles, than those which had previously lived there.
Los Colorados Formation, the imposing red cliffs of the ‘Moon Valley’, extending into Talmpaya, La Rioja province, is the culmination of this last period.
Finally much later, perhaps some ninety million years ago, the movements geologically known as ‘orogenesis andina’, or mountain formation, actually began. These movements in turn, produced balancing movements, fractures, folds, landslides, and the ascension and descension of ancient crystal blocks, forming the hills that today surround the region and the most recent layers of sediments. Since the large reptiles had already disappeared in the Holocene era, some 10,000 to 12,000 years ago, the valley was populated by pumas, guanacos, Creole hares, and a new type of animal--the birds. Descendants of the dinosaurs-the most spectacular birds of this valley are the condors and the South American ostrich. On the contrary, of the ‘true reptiles’, only the small lizards and some poisonous snakes (the coral and yarara) remain.
Man arrived here only a few million years ago and decorated the zone with his rock-paintings or petroglyphs and scattered his arrowheads in the area. Bear in mind that the first scientists only appeared in the valley in the second half of the last century whereas, approximately one decade ago, the recording of the last mutation of fauna coincided with the arrival of the first tourists, who came to see this mysterious ‘Valley of the Moon’
The existing infrastructure consists of nothing more than a small house for the park rangers and an onsite museum. Travelers may, and it is strongly suggested they bring their own provisions, beverages, sunblock, etc. or whatever they feel necessary.. The tour around the park (40 km). Visitors are accompanied by a park ranger in their own vehicle, in a caravan with other cars, taking about four hours. Travelers can find lodgings in the charming village of San Agustin of Valle´ Fertil, or Pataquia, and Villa Union.

Text © Pirelli Guide of Argentina