The source of the Alagón River Nature · Frades de la Sierra, Guijuelo, Salamanca The Alagón River rises in the district of Frades de la Sierra, in Salamanca, and is a right-bank tributary of the Tagus; after passing Monleón, it crosses into the province of Cáceres, passes through Coria and delivers its waters to the Tagus near Alcántara. Already in Cáceres territory, its waters are impounded in three reservoirs: Gabriel y Galán, the largest in capacity, which regulates flow and generates electricity; El Pontón, in Guijo de Granadilla; and Valdeobispo, for irrigation. The PRSA1 trail, the Ruta del Alto Alagón, follows the river's course through its Salamancan stretch over twelve stages and eighty kilometres, from its source in Frades to its entry into Cáceres territory, passing through Endrinal, Monleón, San Esteban de la Sierra, Valero, Garcibuey and Sotoserrano, on the way to the Sierra de Francia. Photo: M. Piola (CC BY-SA 3.0) What to see and do in Frades de la Sierra