fig? /The source of the river Ebro is in Fontibre (Cantabria), from the Latin words Fontes Iberis, source of the Ebro. Close by is the big artificial lake "Embalse del Ebro" created by the damming of the river. The upper Ebro rushes through rocky gorges in Burgos Province. Flowing roughly eastwards it begins forming a wider river valley of limestone rocks when it reaches Navarre and La Rioja thanks to many tributaries flowing down from the Iberian System on one side, and the Navarre mountains and the western Pyrenees, on the other. There, the climate (the valley being isolated from sea air masses by surrounding mountains) becomes progressively more continental, with more extreme temperatures and drier characteristics, and therefore typically experiencing hot (sometimes very hot) and dry summers which closely resemble summers seen in arid and semiarid climates.Karst geological processes shaped the landscape of layers of soluble carbonate rock of extensive limestone bedrock formed in an ancient seabed. Aragonite, a mineral named for Aragon, attests to the fact that carbonates are abundant in the central Ebro Valley.The valley expands and the Ebro's flow then becomes slower as its water volume increases, flowing across Aragon. There, larger tributaries flowing from the Central Pyrenees and the Iberian System discharge large amounts of water, especially in spring during the thawing season of the mountain snow. As it flows through Zaragoza the Ebro, is already a sizeable river. There, the Basilica of Our Lady of the Pillar stands next to the Ebro. The soils in most of the valley are primarily poor soils: calcareous, pebbly, stony, and sometimes salted with saltwater endorheic lagoons. The semi-arid interior of the Ebro Valley has either drought summers and a semi-desert climate with rainfall between 400 and 600 millimetres (16 and 24 in), with a maximum in the fall and spring. It is covered with chaparral vegetation. Summers are hot and winters are cold. The dry summer season has temperatures of more than 35 °C (95 °F), occasionally reaching over 40 °C (104 °F). In winter, the temperatures often drop below 0 °C. In some areas the vegetation depends heavily on moisture produced by condensation fogs. It is a continental Mediterranean climate with extreme temperatures. There are many ground frosts on clear nights, and sporadic snowfalls.The biomes are diverse in these Mediterranean climate zones: Mediterranean forests, woodlands, and scrub. Hinterlands are particularly distinctive on account of extensive sclerophyll shrublands known as maquis, or garrigues. The dominant species are Quercus coccifera (in drier areas) and Quercus ilex. These trees form monospecific communities or communities integrated with Pinus, Mediterranean buckthorns, Myrtus, Chamaerops humilis, junipers, Pistacia, Rosmarinus, Thymus, etc.The hinterland climate becomes progressively more continental and drier, and therefore there is an end from extreme temperatures accompanied by slow-growing dwarf juniper species to unvegetated desert steppes as in "llanos de Belchite" or "Calanda desert".The mountain vegetation is mostly coniferous forests that are drought adapted, and trees in the genus Quercus with different drought tolerance in the wetter highlands.Halophiles extremophile characteristic communities are frequent in endorheic areas such as lagoons and creeks, which are Tamarix covered and include endemic species of bryophytes, chenopodiaceas, plumbaginacea, ruppiaceaes, Carex, lythraceaes, asteraceaes, etc. Their presence is related to the marine origin of the Ebro valley and the extensive marine deposits in the same area.After reaching Catalonia, the Ebro Valley narrows, and the river becomes constrained by mountain ranges, making wide bends. Massive dams have been built in this area, such as the dams at Mequinenza, Riba-roja, Flix. In the final section of its course the river bends southwards and flows through spectacular gorges. The massive calcareous cliffs of the Serra de Cardó range constrain the river during this last stretch, separating the Ebro Valley from the Mediterranean coastal area. After passing the gorges, the Ebro bends again eastwards near Tortosa before discharging in a delta on the Mediterranean Sea close to Amposta in the province of Tarragona.