Pedra do Altar – triangulation station

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Pedra do Altar (altar’s stone) triangulation station (584 m high) is a remarkable spot, since it allows you to see an extensive landscape of the Estremenho Limestone Massif in several directions.

For the north and east quadrants we have an overview of the polje de Minde and, in the distance, of the plateau of S. Mamede. To the southeast comes Aire mountain range and on the background is Tagus Tertiary Basin, uneven with respect to the Estremenho Limestone Massif.

To the west an overview of the Alvados depression, bounded by the escarpment of Alvados fault extending along NW-SE and by the hardness relief of tectonic origin known as Castelejo. To the south-west we observe the development of the plateau of Sto. António, and, at a great distance, is Montejunto mountain.

Geologically, this observation point is in an area of interaction between two normal faults reactivated (thrust) during the Paleogene and Neogene; to the south, the fault of Sto. António and to the northeast, the fault of Pena Falsa. As a result of this interaction the limestone basins of the Middle Jurassic are quite fractured and verticalized due to tight folds, resulting in the development of an extensive karren field and conditioned the very marked relief forms of this region.

Depression – landform sunken or depressed below the surrounding area.

Fault –cracks in the Earth's crust where movement occurs on at least one side.

Fold – formed when one or several originally flat and planar surfaces, such as sedimentary beds, become bent or curved as a result of plastic (e.g. permanent) and ductile deformation.

Jurassic - geological period in which the dinosaurs dominated and the development of vegetation was abundant. It lasted about 54 million years, roughly between 208 to 144 million years ago.

Lapiaz or karren field - common landscape in limestone areas, with many grooves due to the dissolution of limestone by rainwater along fractures and cracks.

Limestone – sedimentary rock composed of calcium carbonate.

Neogene – part of the Upper Cenozoic, between 23.5 and 1.75 million years. Includes the Miocene and the Pliocene.

Paleogene - the beginning of the Cenozoic Era. It began 65 million years ago (My) and lasted until 23.5 My. Includes the Paleocene, the Eocene and the Oligocene periods.

Polje – limestone relief form consisting of an elongated and long depression generally flat bottom. Often it has a very steep slope corresponding to a fault. In rainy periods it often becomes a temporary pond.

Tectonics - study of rocks deformation that make up the Earth's crust and the forces that produce such deformation at a global scale.

Thrust - formed by horizontal compressive stresses and so cause shortening of the crust. Since the hangingwall moves up relative to the footwall, most of these faults place older rocks over younger ones.