The Nave dos Cordeiros is a large karst depression located in the limestone region of the Barrocal, and it is classified as a polje. It stretches approximately 5 kilometers in length and is oriented in an east-west direction, similar to the Nave do Barão, from which it is separated by a small elevation known as Portela.

The limestones and dolomites that form the “Nave” date back to the Lower Jurassic period, approximately 201 to 175 million years ago. The floor of the depression is covered with colluvium and red earth, which absorb rainwater and create temporary puddles during rainy seasons. In the nearby villages of Nave dos Cordeiros and Charneca da Nave, there are also rocky elevations made of oolitic limestones. This type of limestone is characterized by small calcareous spheres that form through the inorganic precipitation of calcite around a nucleus, which can be a grain of sand or a shell fragment.

The Alte stream flows through this karstic depression, originating at Fonte Grada and eventually flowing into the Vala Grande. During particularly rainy winters, the groundwater level rises and intersects with the surface. This causes the bottom of the Nave to fill with water from springs located at its lowest points and along its slopes.