The watershed between the Ebro and the Duero Nature · Villafranca Montes de Oca, Montes de Oca, Burgos The Montes de Oca mark the line that separates the basins of the Ebro and the Duero: to the north the waters go down to the Oca and the Ebro, to the south to the Arlanzón and the Duero. The route crosses the ridge between 1,000 and 1,100 metres of altitude. Photo: Cornava (CC BY-SA 3.0) What to see and do in Villafranca Montes de Oca