Tagus and the Guadiela”. Journey to the Alcarria, Camilo Jose Cela. Nowadays, Entrepeñas has a reservoir located in the lower Alcarria of Guadalajara in the course of the Tagus. It was inaugurated in 1956. Besides the Tagus, other contributing rivers are Valdetrigo, Barranco Grande, La Solana and Ompolveda, among others. Camilo Jose Cela toured the area before it was built.