The source of the Ucero at la Galiana Nature · Ucero, Tierras del Burgo, Soria At the end of the canyon, beside the Galiana cave, a spring rises that gives origin to the río Ucero. In that same place the río Lobos dies, which for much of the year runs dry along the bottom of the gorge. Photo: Javier Casado Tirado (CC BY-SA 3.0) What to see and do in Ucero