The Köpet Dag, Kopet Dagh, or Koppeh Dagh, also known as the Turkmen-Khorasan Mountain Range, is a mountain range on the border between Turkmenistan and Iran that extends about 650 kilometres (400 mi) along the border southeast of the Caspian Sea, stretching northwest-southeast from near the Caspian Sea in the northwest to the Harirud River in the southeast. In the southwest it borders on the parallel eastern endings of the Alborz mountains being together part of the much larger Alpide belt. The highest peak of the range in Turkmenistan is the Mount Rizeh, located at the southwest of the capital Ashgabat and stands at 2,940 metres (9,646 ft). The highest Iranian summit is Mount Quchan at 3,191 metres (10,469 ft).