It was only in the early 1990s that the petroglyphs of the Coa Valley obtained Portuguese and international attention. In 1992 the government planned to flood the area as part of a dam project. After the river level was lowered and an archaeological survey was made many previously unknown sites were exposed. This brought about cessation of the project and the sites are preserved for posterity as the Coa Valley archaeological Park. The site, dating to the Paleolithic, was declared a UNESCO world Heritage Site in 1998.
The earliest petroglyphs are believed to have been done between 8,000-20,000 years ago, though the Upper Paleolithic dating has been challenged. The dating has been based on three things:
1- Finding an animal figure depicting a species existing In a restricted period of time, such as a horse, deer or ibex.
2- Finding petroglyphs below ground level and dating them through stratigraphy to associated sites of the same period.
3- Finding evidence of occupation; until radiocarbon dates from Coa Valley sites are provided the actual dating remains controversial.
Another characteristic feature of the landscape are the rocky formations outcropping through the predominantly low and open vegetation: granites upstream from Santa Comba, schist downstream to the Douro. Erosion acts upon these different bedrocks in different ways. The granitic plateaus, cut by deep ravines, feature spaced accumulations of large round boulders.
Archaeology Study Unit 