The southern high mountain ranges, part of the Basque mountains, that form a continuous barrier with passes not lower than 600 m AMSL, forming the water divide of the Atlantic and Mediterranean bassins. These ranges are divided from west to east in Ordunte (Zalama, 1390 m), Salbada (1100 m), Gorbea (1481 m) and Urkiola (Anboto, 1331 m).
The middle section which is occupied by the main river's valleys: Nervion, Ibaizabal and Kadagua. Kadagua runs west to east from Ordunte, Nervion south to north from Orduña and Ibaizabal east to west from Urkiola. Arratia river runs northwards from Gorbea and joins Ibaizabal. Each valley is separated by medium mountains like Ganekogorta (998m). Other mountains , like Oiz, separate the main valleys from the northern valleys. The northern rivers are: Artibai, Lea, Oka and Butron.
The coast: the main features are the estuary of Bilbao where the main rivers meet the sea and the estuary of Gernika (Urdaibai). The coast is usually high, with cliffs and small inlets and coves.
The climate is oceanic, with high precipitation all year round and moderate temperatures, which allow the lush vegetation to grow. Temperatures are more extreme in the higher lands of inner Biscay, where snow is more common during winter.
