The commune of Gasques is located on a serre (a narrow, elongated ridge several kilometers long, lying between two parallel valleys cutting into a limestone plateau) bounded by two rivers, the Séoune and the Barguelonne, which flow from northeast to southwest toward the Garonne. This section of the plateau has been incised by small tributary streams, creating the emblematic landscape of the Barbe stream valley, with its cliffs and discreet springs.