The Emba River in west Kazakhstan rises in the Mugodzhar Hills and flows some 400 miles (640 km) southwest into the Caspian Sea. It flows through the north of the Ust-Urt plateau, reaches the Caspian by a series of shallow lagoons, which were navigable in the 18th century. The lower course traverses an area of salt domes and the petroleum-rich Emba fields. It is considered by some experts as a boundary between Asia and Europe.