The Sierra de las Quijadas National Park () is a national park located in the northwestern part of the Argentine province of San Luis. It was established on December 10, 1991, to protect the natural features, representative of the Semiarid Chaco and the High Monte ecoregions.
Climate
In San Luis, the ecotone between the mountains and the Chaco is located west of the isohyet and covers about . The climate of the area is semi-arid and is characterized by sharp temperature variations, both seasonal and daily. The average annual maximum temperature is , while the minimum is . The annual average temperature is . The maximum monthly average temperature is and for the month of January; the minimum is for the month of July. The average value of relative humidity varies between 48% in August–September to 64% in April–June; the annual average is 55%. Precipitation is scarce and unevenly distributed throughout the year. There are two seasons: dry during winter and wet from late spring to early autumn.
Geology
Sierra de las Quijadas is located in the San Luis Basin, whose surface is composed of sedimentary, metamorphic, and igneous outcrops of various ages. The basin is bounded by the Sierra de San Luis to the east, while to the west the basin is presumed to be subsurficially connected to the Triassic basins of the Mendoza and San Juan provinces. To the north, the basin extends to Marayes de San Juan. It is an anticlinal structure, of roughly elliptical shape whose major axis is oriented meridionally. A large fracture extends in the north–south direction, subparallel to the current course of the Desaguadero River. Along this fracture, the Quijadas range has been lifted.
Geologic origin
The geologic origin of the Quijadas is composed of three stages: infill, uplift and erosion. 120 mya, the present location of the Quijadas was occupied by a sedimentary basin, flanked by two highlands. One of them is the Sierras de San Luis. Another is a range that had existed along the current course of the Desaguadero River. The basins began to be filled with fluvial and aeolian sediments, eroded from the highlands. The process lasted some 20 Ma, which resulted in the basin being completely filled 100 mya. The following 75 Ma are missing from the geologic record and are assumed to be a period of calm. During the Tertiary, the layers that had been deposited 120–100 mya were raised and folded by the tectonic processes associated with the formation of Sierras Pampeanas. The uplift began 25 mya, and the Quijadas still rise, as the South American Plate continues its westward migration. Concurrently with the uplift, erosion became a major factor, which created the modern valleys and ravines, such as the Potrero de la Aguada valley.