Sierra de las Quijadas

Sierra de las Quijadas National Park protects 150,000 hectares of dramatic arid canyon and desert landscapes in the Puyén depression of San Luis Province, central-western Argentina. Established in 1991, the park is renowned for its spectacular red sandstone canyons, arches, and badlands, as well as one of the most important Cretaceous fossil sites in Argentina. The park's erosional landscape—featuring massive amphitheaters called 'Potrero de la Aguada'—rivals in spectacle the canyon landscapes of the American Southwest and offers exceptional geological and palaeontological interest.

The park protects Chaco-Monte transitional ecosystems and their associated fauna. Guanacos are the most visible large mammal, grazing the arid scrubland. Pumas and Geoffroy's cats hunt the rocky terrain. Maras (Patagonian hares), viscachas, and armadillos are commonly seen. The bird life includes condors that roost on the canyon walls, as well as burrowing owls, scaled doves, and various raptors. Reptiles thrive in the hot, arid conditions—several species of lizard and the venomous rattlesnake (Crotalus durissus) are present. The canyon also provides habitat for bats in cliff crevices.

The vegetation reflects the semi-arid Monte-Chaco transition zone. Jarilla (Larrea divaricata and L. cuneifolia) dominates the open scrubland. Algarrobo (Prosopis flexuosa) trees grow along dry watercourses. Opuntia cacti, bromeliads (Dyckia spp.), and various thorny shrubs characterize the canyon walls and rocky slopes. The park's low rainfall (less than 300 mm/year) supports a flora adapted to extreme drought stress. Spring brings a brief explosion of wildflowers when rains briefly moisten the desert soils.

The park's geology is the primary attraction for researchers. The canyon system has exposed a sequence of Cretaceous sedimentary rocks (approximately 110–115 million years old) of the Lagarcito Formation. These red and brown sandstones and mudstones were deposited in a lake and river delta environment during the early Cretaceous. The fossil beds within these formations have yielded extraordinary finds including dinosaur bones, pterosaur tracks, and abundant invertebrate fossils. The canyon walls rise up to 400 meters above the valley floor, exposing tens of millions of years of geological history.

Sierra de las Quijadas has an arid to semi-arid continental climate. Summers (November–March) are very hot, with temperatures regularly reaching 38–42°C in the canyon. Winters are mild to cold, with frost possible in June–August. Annual rainfall averages 300–400 mm, concentrated in summer thunderstorms that can cause flash flooding in the canyon systems. The low humidity makes the heat more tolerable, but visitors must carry ample water. Wind is common throughout the year. The combination of high temperatures and dry air creates excellent preservation conditions for fossils.

Rock art sites within the park indicate human presence dating back several thousand years. The Huarpe people, indigenous inhabitants of the San Luis and Mendoza region, utilized the park's area for hunting and gathering. Spanish colonial forces passed through the region in the 16th century as they explored the Andean foothills. The area was subsequently used for cattle and goat ranching, which caused significant vegetation degradation. The name 'Las Quijadas' (The Jawbones) may refer to the shape of the mountain range or to bones found by early settlers.

Sierra de las Quijadas National Park was established in 1991, recognizing both the geological and palaeontological significance of the canyon system and the ecological importance of the Monte-Chaco ecosystems. Palaeontological research in the park began in earnest following its protection, with Argentine and international teams excavating the Cretaceous fossil beds. The park administration has worked to balance scientific access with visitor tourism and conservation of the fragile desert ecosystems. Fossil protection laws strictly prohibit unauthorized collection.

The Potrero de la Aguada circuit is the park's signature experience—a 15-km round-trip trail descending from the canyon rim into the spectacular red sandstone amphitheater. The trail crosses seasonal stream beds and passes through the narrow canyon system before opening into the vast desert bowl. Dawn and dusk visits are recommended for dramatic lighting and wildlife activity. The palaeontological site with exposed dinosaur tracks and bones is visible from designated viewpoints. The canyon walls offer rock climbing for experienced climbers. Condor sightings are regular from the rim.

The park visitor center is located on Route 147, approximately 100 km northwest of San Luis city. The visitor center houses an excellent palaeontological exhibit explaining the Cretaceous fossils found in the park. Guided walks to the Potrero de la Aguada are led by park rangers. An entrance fee is charged. Camping is available at a designated campground near the visitor center. The park is day-accessible from San Luis city. Water must be carried as there are no reliable water sources within the canyon. Summer visits require very early starts to avoid midday heat.

Fossil poaching—illegal collection of Cretaceous fossils—has historically been a problem and remains a concern, requiring regular ranger patrols. Overgrazing by goats from neighboring properties degrades native vegetation along the park boundaries. The arid ecosystem is extremely sensitive to disturbance, with vegetation recovery taking decades after damage. Off-road vehicle use damages soil crusts and vegetation. Climate change projections indicate increasing drought frequency for the San Luis region, which would further stress the park's water-limited ecosystems.