Mashhad is located in the north-east of Iran close to the Soviet and Afghan borders, and is the capital of the Ostan (province) of Khorasan. The city is situated at about 3,000 feet, at the eastern end of a fault-bounded tectonic depression filled with quarternary sediments and drained by the Atrek Rud2to the west (into the Caspian) and by the Kashaf Rud to the east. This corridor-like depression separates two branches of a fold mountain system, known as the Elburz. The southern branch of this mountain system named the Kuh-i-Aleh and Kuh-i-Binalud3, is composed of N, esozoic limestones and igneous rocks and rises to 10,000 feet, whilst the northern branch, the Kuh-i-Hesar Masjid built mainly of cretaceous limestones, slopes west-east from 10,000 feet to 6,000 feet. This latter range separates the Atrek- Kashaf corridor from the steppes of Central Asia to the north, and it is along its north-facing flanks that the Soviet border is aligned. To the south and west of the Kuh-i-Aleh, the Jajarm-Isfarain basin forms the other main lowland area of northern Khorasan. (Figs. 1 and 2) South of this fold mountain area stretches the central plateau of Iran over which are developed the deserts of the Kavir5 and the Southern Lut6 occupying over two-thirds of the province of Khorasano The eastern edge of this desert plateau is bounded by a low range of mountains running north-south, forming the boundary between Iran and Afghanistan.