The rocks here belong to the Ischigualasto Formation, laid down in the Late Triassic, between roughly 231 and 226 million years ago. Walk the badlands and you are walking through layers of that lost world. In the Carnian age, this was no desert at all but a volcanically active floodplain laced with rivers and drenched by seasonal rains. Petrified trunks of an ancient conifer, more than 40 meters tall in life, still lie scattered across the ground, alongside the fossilized traces of ferns and horsetails. The harsh, lunar emptiness of today is a disguise. Beneath it lies the memory of a green and humid place teeming with life.

Most of the fossils here are not dinosaurs at all. Beaked reptiles called rhynchosaurs and mammal-like cynodonts dominate the record. But among them are some of the oldest known dinosaurs in the world, and that is what makes Ischigualasto extraordinary. In the early 1990s, paleontologists working these slopes found Eoraptor lunensis, a slender, meter-long animal near the very root of the dinosaur family tree. They also found Herrerasaurus, a sharp-toothed predator that is the most numerous dinosaur in the formation; close relatives like it account for nearly three-quarters of all the meat-eaters recovered. Here, captured in stone, is the moment dinosaurs were just beginning their rise toward dominance.

Science came slowly to this remote ground. The first paleontological notes date to 1930, and by 1941 researchers had identified some seventy species of fossil plants. The breakthrough came in 1958, when Dr. Alfred Sherwood Romer, a Harvard expert on early mammals, walked the badlands and uncovered fossil beds so rich he called them simply extraordinary. The discoveries that followed drew researchers from around the world and rewrote the early chapters of dinosaur history. Even the park's name reaches back further still: Ischigualasto may come from the Diaguita language, said to mean dead land, though some scholars trace it instead to Huarpe roots, the Indigenous peoples whose words still cling to this landscape.

At about 1,300 meters above sea level, the park sprawls across the western edge of Argentina's Central Sierras, its sparse desert scrub covering only a tenth or so of the ground. The rest is rock, sculpted into otherworldly shapes by water and relentless wind: a formation called the Sphinx, another known as the Mushroom, and the deep red cliffs of Las Coloradas. The climate is unforgiving, with summer heat reaching 45 degrees Celsius and a steady afternoon wind that sometimes builds into the fierce, dry Zonda. Established as a protected area on November 3, 1971, Ischigualasto was inscribed as a UNESCO World Heritage Site in 2000, together with neighboring Talampaya just across the line in La Rioja Province.