The geographical heart of Alava is the Zadorra basin, just as the basins of Guipúzcoa, Vizcaya and Navarre are the basins of the Oria, the Ibaizábal and the Arga. Almost the entire Alavese hydrographic network discharges its waters into the Mediterranean, via the Ebro river. Only a small part flows into the Bay of Biscay, 1/8 of its total surface area. These Atlantic parts are the valley of Aramayona, to the east of Mount Albertia, and those of Arceniega, Ayala, Llodio, Oquendo, Arrastaria and part of Urcabustaiz enclosed the mountains of Altube, Guibijo and Sierra Salvada.
See GEOGRAPHY (Voice Index).