The River Ebro. It serves as the boundary Alava and Burgos and Logroño for over one hundred kilometres. It reaches the Basque Country through the Besantes gorge, in the Sobrón mountains, in a W-E direction. It passes through Bergüenda and Puentelarrá, where it heads SE towards Fontecilla and Comunión. At Buradón it makes its way through the Sierra de Toloño and the Obarenes Mountains to enter the Rioja. Its banks are steep in the Sobrón mountains and in the Conchas de Haro, flat in the Miranda plain and abrupt in the Rioja. The Alavese rivers Purón, Omezillo, Bayas, Zadorra and Inglares flow into it.