The Kopet Dag, Kopet Dagh, or Koppeh Dagh, also known as the Turkmen-Khorasan Mountain Range is a mountain range on the frontier between Turkmenistan and Iran, extending about 650 kilometres along the border, east of the Caspian Sea. The highest peak of the range in Turkmenistan is southwest of the capital Ashgabat and stands at 2,940 metres. The highest Iranian summit is 3,191 metres .
This mountain range has a ski resort, officially opened by the former president of Turkmenistan, Saparmurat Niyazov. Despite the lack of snow in the Kopet Dag mountains, Niyazov was determined to build a major resort there.
The Kopet Dag Range is a region characterized by foothills, dry and sandy slopes, mountain plateaus, and steep ravines. The Kopet Dag is undergoing tectonic transformation, and is subject to severe earthquakes. Earthquakes exceeding seven on the Richter scale have been recorded.
The foothills of the Kopet-Dag near Ashgabat are the site of the remains of the ancient Parthian city of Nisa (Nessa, Nusay).