Known as Singilis in Latin, it bears a modern name derives from the Moorish rendering of the Roman name: Sinyil, Sannil, and Sinnil.

The source of the Genil is in the Sierra Nevada, north of its highest peak Mulhacén.

In the latest Tortonian and the middle and late Turolian (9.0–5.3 Ma) this was an endorheic basin.

Rivers flowed from the east and southwest into a central lake with no exit.

Some time later, the Genil river changed course to flow west, where it joined the paleo-Cacin system, and the basin became exorheic.