Cerro Alcázar, Natural monument in Calingasta Department, Argentina

Cerro Alcázar is a hill on the western flank of the Sierra del Tontal, in Calingasta Department, western San Juan Province, Argentina. Its capricious forms, carved by wind and rainfall, come from Triassic sedimentary rocks laid down at the start of the Mesozoic era; their colouring and castle-like shapes led to the name.

The hill is made of sedimentary rock laid down at the start of the Mesozoic era, and its colours come from Triassic-age sediments. Wind and rainfall erosion later carved the shapes that resemble a fortress. In 1993, decree 0271-6-93 declared it a Natural Monument of San Juan Province.

The name comes from Arabic through Spanish, meaning fortified palaces, which reflects how the rocky walls resemble medieval castle structures. When you walk around the formation, you can see why people chose this name for the place.

Cerro Alcázar lies on the western flank of the Sierra del Tontal, in Calingasta Department, and is reached directly from Provincial Route 412, 22 km from Barreal and 155 km from San Juan. The protected area covers the hill and its immediate surroundings, so walking is confined to the marked route and the road verge.

The protection came through provincial decree 0271-6-93, which declared the hill a Monumento Natural of San Juan. The name Alcázar comes from the Arabic al-qaṣr, "the castle", because the eroded rock walls resemble a medieval fortress.