a tectonic basin in Iran, separating the Kopet Dagh from the central ranges of the Turkmen-Khurasan mountains.
The region includes the valleys of the Atrak and the Kashafrud (left-bank tributary of the Harirud), as well as the flat watershed between them (elevation, 1,350 m) and adjacent foothill plains. Length, about 275 km; width, 15–30 km. The valley is composed of proluvial and alluvial (frequently loesslike) deposits and is noted for high seismic activity. Precipitation totals about 200 mm per year. Landscapes are predominantly of the desert foothill type. At the bottom there is an almost uninterrupted chain of oases with the towns of Meshed, Quchan, and Shirvan. The valley is the main region of irrigated agriculture in northeastern Iran. Cotton, opium poppies, vegetables, and cereals are cultivated, and there are numerous orchards and vineyards.