Slate quarries of the Casoio valley Curiosity · Carballeda de Valdeorras, Valdeorras, Ourense Image of Carballeda de Valdeorras, not of the place itself. The discovery of major slate deposits in the 1950s in the valleys of the Casoio and Candís rivers launched an industry that made Valdeorras the largest slate-producing area in Spain. Photo: Robbychucky (CC0) What to see and do in Carballeda de Valdeorras