During the
Miocene era, the river's valley was actually an arm of the sea that connected the waters of the Mediterranean with those of the
Atlantic Ocean through the Bética depression (now the valley of the
Guadalquivir). In the
Pliocene, this connection was severed by the creation of the Sierra of
Mijas and the
Montes de Málaga, while also creating the geologically isolated Sierra of
Cártama. Throughout the rest of the Pliocene, the river basin eventually took on its current form. ==Tributaries==