The Guadyerbas is a short river in the centre of the Iberian Peninsula, a tributary of the Tiétar, belonging to the Tajo river basin. It rises at an altitude of 1,200 metres above sea level, south of the Cruces mountain (El Piélago), in the San Vicente mountain range. The watercourse, which runs through forests of junipers, poplars and holm oaks, flows towards the Navalcán reservoir and 7 kilometres further on joins the river Tiétar.