Tehran has developed on recent sediment and quaternary. Geological maps confirm that quaternary and Pliocene alluviums and moraine deposit have developed in Tehran desert.
Bed rock. The bed rock of Tehran is the Tertiary formations, mostly Eocene lava, showing in the mountainous areas in the north of the city. The younger sediment have formed on this bed rock. The bed rock of the eastern heights in Sehpayeh and Bibi Shahrbanoo mountains have been formed from the dolomite limestone from Triassic and Cretaceous ages.
Hezardarreh formation. The name of the formation, literally “Bad land morphology ” has been inspired by the geomorphologic properties of its surface and the existence of the multitude of its erosional valleys of great density. This formation widens and rises and increases in bulk at Ghoochak defile in the northeast of the city. Its alluvial substances mainly consist of alluvial sediment and alluvial talus and volcanic rocks from Eocene age.
- Young alluvial fans. This formation includes deposits of conglomeratic young alluviums. The stones of this formation consist of homogenous conglomerates made of sand and Grave land pebble size class. The outcrop of the young Alluvial Fans of Tehran is expanded towards the southern half of the city. A great part of Tehran has been built on this formation. The maximum thickness of the alluvial Fans is estimated to be 60 meters. These alluvial Fans are highly penetrable; they form the greater part of the aquifers of the north of Tehran.
- Tehran’s river alluviums and alluvial plain. This formation is the youngest stratigraphical unit of Tehran formed as alluviums and river deposits. This formation is divided into two different stratigraphical alluvial plain units:
A) Khorramabad alluvial formation. This formation has covered the formation of the older alluvial fans in the south of Tehran, forming a fairly smooth plain. In the northern and eastern parts, the sand is richer. The southwest of the plain is dominated by fine grain material such as clay and silt.
B) River alluviums unit. The most recent alluviums of alluvial levels in Tehran are formed by the deposits of the flood plain of rivers consisting Grave land pebble size clasts. These materials have an alluvial origin and are not very hard.