The Bardenas is in the southeast of Navarre, bordering Aragon. It is located in the middle of the depression of the Ebro valley at the foot of the mountains of the Yugo and the Zaragoza region of Cinco Villas. It is 45 km (28 mi) from north to south and 24 km (15 mi) east-west and at an altitude ranging between 280 and 659 m (919 and 2,162 ft). Its area is 41,845 hectares (418.45 km2; 103,400 acres). There are only sixteen municipalities, of which thirteen are in Navarre and three in the province of Zaragoza. The Navarrese are Valtierra, Arguedas, Carcastillo, Santacara, Mélida, Rada, Caparroso, Villafranca, Cadreita, Tudela, Cabanillas, Fustiñana and Buñuel, while the Zaragozan are: Tauste, Ejea de los Caballeros and Sádaba.
Las Bardenas is divided into several distinct areas which mainly include two, Black Bardena and White Bardena, but there are other smaller areas of great singularity.
It is the central area and more desert. Its relief is characterized by extensive plains and deep gorges through which rivers flow. This Bardena owes its name to the presence of white salt that extends over the surface due to the abundance of gypsum in the soil.
The White Bardena divides into two, the White Lower and Upper White. The first is the most depressed and the second extends from Pisquerra and Eguaras to Carcastillo.
Black Bardena is situated in the southeastern part of the territory on the border of the Autonomous Community of Aragon. Formed by plateaus of different altitudes and cut by rivers flowing at the bottom of the cliffs, this part of the Bardenas is covered with vegetation.
There is a central plateau that lies 100 m (330 ft) above the surrounding area where corn is grown. It is formed by Tertiary and Quaternary soils that were raised by pressure associated with the creation of the Pyrenees and the mountains of Central Spain that caused the collapse of the Ebro basin forming an inland sea enclosed by the Catalan Coastal Range. Sediments laid down were then eroded from the Eocene onwards. These formed gravel and sandstone that stayed at the top, fine sand, clay, and limestone occupy the lower slopes. Clay remained in the centre and limestone and gypsum formed at the edges. The gravel, sandstones, and clay were all associated with alluvial deposits. Mixtures of sandstone and clay formed two mountain ranges between the centre and perimeter. The sediments may have been four metres (13 ft) thick. Ten million years ago, the basin opened to the Mediterranean Sea and drained, leaving the Ebro, which began water erosion along the southern perimeter, which left the remaining land relatively flat. The folding effect of erosion is caused by alternate soft and hard materials. If the layers are horizons, then the Cabezas became isolated.
