 It begins in the Sistema Ibérico range and flows north through the municipalities of Rábanos, Villafranca Montes de Oca, Valle de Oca, Alcocero de Mola, Prádanos de Bureba, Briviesca, Vileña, the shire of Bureba and Oña.The Oca River rises in the "comarca" of Montes de Oca, near the town of Rábanos.Near its source, the river passes through the narrow, rock-lined gorge of La Hoz.