River Bayas. It rises in the upper part of the Zuya valley, to the south of Gorbea. The contribution of several sources, Ubegi, Lapurzulo and Azoteta - in Vizcaya - swell the Pedrobaso. The latter, together with the Arralde, form the upper west basin of the Bayas. The Errerías and Riakorba ravines collect the waters on the eastern side. These two branches join at Ezkarai to form the River Bayas. At Marquina (A) it receives the contribution of the Ugalde, which flows down from the Gorbea. In Murguía, the Aziturri, and from Domaikia the Txikaran (Arrato mountain range). The ravine formed by the Arangachas, Guillarte, Marinda and Cuartango mountains provides its waters with the Fuentes, Yartos, Vadillo and other ravines. The River Bayas descends through the Zuya valley, passing through Marquina, Sarría, Murguía and Victoriano de Zuya. From this point it runs in a south-westerly direction as far as Abornicano (Urcabustaiz). It heads south and enters the Cuartango valley via Andagoya and Anda. Its middle course runs through Cuartango, via Echábarri de Cuartango, Urbina de Eza, Zuazo de Cuartango and Apricano. Beset by the Badaya mountain range to the east and the Arcamo mountain range to the west, it enters Pobes (Ribera Alta) through the Techa pass. South of Pobes it continues through more open terrain. It leaves Alava near Ribavellosa and flows into the Ebro below Miranda (B).