For Valle d 'Opel or Val d'Opello we mean the stretch of valley that, from Ca' de l'Aért, descends towards the locality called Sbardellata and represents the highest stretch of the so-called Valle dei Prigionieri which flows directly into the river Serious. This toponym appears in a few topographical maps because its furrow over the centuries has been invaded by enormous mounds of roère, the well-known dumps of debris of veins from coti, an unmistakable sign of the centuries-old mining activity carried out here by man. Of the existence of this valley, of the antiquity and of the consistency
of the mining activity that took place there, many documents that speak of quartz stones starting from the century are authentic. XII.
On the basis of the archival documentation, the Valle d'Opel can be considered to be the best known and the oldest station for the production of coti stones.
In addition to the oldest, the veins of Val d 'Opel were perhaps also those which, according to a consolidated oral tradition, never demonstrated but likely, communicated with the veins of Val Predina or Val Calchera in the territory of Cenate Sopra, located more or less at the same altitude on the southern side of Mount Misma and which probably exploited the same veins of stone. Among the old coderócc (quarrymen of coti stones) it was said that in the veins located upstream of the Sbardellata one could enter from the Pradalunga side and exit on the opposite side of Cenate Sopra.