This geosite, classified as Pedras Ruívas Local Natural Monument, corresponds to an area of approximately 58 ha, delimited between the northern proximal coastal sector of the Rego de Fontes Fort and the southern end of Praia Norte, with an extension of approximately 1500 meters along the shoreline. In this area essential elements for the interpretation of the geological and cultural history of the territory, that began about 500 million years ago, are preserved . While trilobite’s trails and other rock marks reveal the history of the Rheic Ocean and its closure, a deposit of silt by the sea indicates the existence of a lagoon about 20 000 years ago. From primitive oceans to ancestral lagoons, the Pedras Ruívas Local Natural Monument is a key area for understanding the evolution of our territory.