Río de Oro is the southern geographic region of Western Sahara. It was, with Saguia el-Hamra, one of the two territories that formed the Spanish province of Spanish Sahara after 1958; it had been taken as a Spanish colonial possession in the late 19th century. Its name seems to come from an east–west river which was supposed to have run through it. The river was thought to have largely dried out – a wadi, as the name indicates – or have disappeared underground.