This space is located on the southern edge of the Ebro basin. This basin was filled with sediment during the Tertiary period, at the same time as Alpine orogenesis was raising the Pyrenees to the north and the Prelitoral mountain range to the south and southeast. In the beginning, it was occupied by the sea and sea sediments were deposited there. Little by little, this basin closed and plaster and salts were deposited. Finally (in Oligocene) it was completely closed and it was filled with continental sediments.

This space is located in the lower course of the river Ebro, where it crosses the Prelitoral mountain range and, a few kilometers, ends at the sea forming the Ebro Delta. The river forms wide meanders and deposits river sediments, mainly clays, gravels and sands, in the form of terraces. The constant dynamics of the river give rise to abandoned meanders, such as the one seen in the south of Flix, and to fit into the terraces themselves. The current level, which is where the riparian vegetation grows, is made up of very recent silts and is some 20 or 30 metres below the high terraces.

Due to the construction of the Flix reservoir, the Ebro river's equilibrium profile changed, and the river's water velocity slowed, also reducing its ability to provide sediment depositing at the edges or protected areas. However, artificial regulation of the river by the Riba-roja and Mequinensa reservoirs has softened the flood regime and, therefore, the silty deposits where the vegetation is settling, are more stable.