What are the Ebro depression and the Pyrenees’ southern terraces?

The Pyrenees mountain range is flanked by broad depressions, with the Ebro depression located to the south.1

The Ebro Depression

The Ebro depression is a large, arid, and sparsely populated interior basin in northeastern Spain. It is characterized by nearly horizontal sedimentary strata, resulting in a landscape that is mostly plain or plateau. The basin is separated from the Meseta Central by the Iberian Cordillera and receives water from numerous tributaries, particularly those originating in the rainy Pyrenees, which contribute the majority of the river's volume.23

The Pyrenees’ Southern Terraces

The Pyrenees descend steeply on their northern side, but on the south, they descend in a series of terraces toward the Ebro River trough. These southern slopes feature a broad, pre-Pyrenean middle depression containing a succession of marine and continental deposits. This area includes secondary outcrops that form the "Exterior Ridges," which constitute the northern rim of the Ebro depression. These southern zones are more highly developed and thicker than their northern counterparts.24