This basin occupies an immense area of north-central Iran, over 200,000 sq km in the rain shadow of the Alborz Mountains. Mahdavi and Anderson (1983) detailed the qanat water supply of the margins of this basin. Intermittent streams drain to several kavirs which are grouped together under this basin for convenience. The principal kavirs are the Damghan Kavir in the north, the Sabzevar Kavir in the north-east and the Kavir-e Bozorg (or Great Kavir) occupying much of the basin, being about 450 km in east-west extent and 250 km in north-south extent. The Kavir-e Bozorg receives waters exiting from other kavirs. The principal streams entering this basin drain the Alborz Mountains and their eastern extensions in Khorasan. The Alborz peaks exceed 4000 m and even to the east the Kuh-e Binalud (36°30'N, 58°55'E) attains 3416 m near Neyshabur (36°12'N, 58°50'E) while the lowest points are at an altitude of 650 m. The Damghan Kavir receives two major streams from the Alborz, the Damghan River and the Hasanabad River, and other streams dry up in early summer. The Sabzevar Kavir has numerous small and temporary streams which feed it as well as two major streams, the Mureh River, 320 km long, and its tributary, the Kalshur River, 240 km long. The Kalshur drains the Kuh-e Binalud and flows west to meet the south flowing Mureh. These rivers drain areas rich in salt domes and samples taken show water to be saline and some streams are fishless. Qanats support fishes in this area although the fish only emerge at night in some cases. Ruttner-Kolisko (1964; 1966) and Ruttner and Ruttner-Kolisko (1972; 1973) studied the chemistry and limnology of natural springs and qanats in a mountain area separating this basin from the Bejestan basin. Several factors were found to affect the limnology. Climatic factors were temperature, precipitation and evaporation, edaphic factors were geology, salt content of soil and intensity of waterflow, and pollution by man and animals was a factor. There was a range in salinity from low (<15 mval/l) to high (>120 mval/l). Qanat discharges in this area were 20-50 l/sec. Springs were small and many were dammed to form small pools for livestock.

These large central basins of Iran were once thought to be desiccating lake basins. However more recent studies have shown that although there may have been shallow lakes, e.g. saline Lake Damghan, and rivers carried more flow and were perhaps more closely linked than today, there was no extensive and continuous freshwater lake over the whole of central Iran that could have facilitated fish dispersal. While the hills received increased rainfall, the central deserts remained arid during Pleistocene "pluvials" and cold phases (Bobek, 1959; Scharlau, 1968; Krinsley, 1970).

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