The mountains of the West Saharan montane xeric woodland ecoregion are found within the Sahara Desert and are predominantly of volcanic origin. They rise from the surrounding flat desert landscape or sand dunes and create islands of moister habitat (guelta) which support flora and fauna. The most important area is the Tassili n'Ajjer Plateau, an outlier of the Ahaggar Mountains in Algeria which supports some near-endemic species and some globally threatened antelopes.