mountain range on the border between Turkmenistan and Iran. It runs northwest–southeast for more than 400 miles (645 km), from near the Caspian Sea (northwest) to the Harīrūd (Turkmen: Tejen) River (southeast). Kūh-e Qūchān (10,466 feet 【3,191 m】), in Iran, is the highest point in the Kopet-Dag proper, although there are higher elevations in the range's outliers in Iran. The important city of Ashgabat, the capital of Turkmenistan, lies in the foothills of the Kopet-Dag.