The topography of Iran consists of rugged, mountainous rims surrounding high interior basins. The main mountain chain is the Zagros Mountains, a series of parallel ridges interspersed with plains that bisect the country from northwest to southeast. Many peaks in the Zagros exceed 3,000 metres (9,843 ft) above sea level, and in the south-central region of the country there are at least five peaks that are over 4,000 metres (13,123 ft).
As the Zagros continue into southeastern Iran, the average elevation of the peaks declines dramatically to under 1,500 metres (4,921 ft). Rimming the Caspian Sea littoral is another chain of mountains, the narrow but high Alborz Mountains. Volcanic Mount Damavand, 5,610 metres (18,406 ft), located in the center of the Alborz, is not only the country's highest peak but also the highest mountain on the Eurasian landmass west of the Hindu Kush.
The center of Iran consists of several closed basins that collectively are referred to as the Central Plateau. The average elevation of this plateau is about 900 metres (2,953 ft), but several of the mountains that tower over the plateau exceed 3,000 metres (9,843 ft). The eastern part of the plateau is covered by two salt deserts, the Dasht-e Kavir (Great Salt Desert) and the Dasht-e Lut. Except for some scattered oases, these deserts are uninhabited.
Iran has only two expanses of lowlands: the Khuzestan Plain in the southwest and the Caspian Sea coastal plain in the north. The former is a roughly triangular-shaped extension of the Mesopotamia plain and averages about 160 kilometres (99 mi) in width. It extends for about 120 kilometres (75 mi) inland, barely rising a few meters above sea level, then meets abruptly with the first foothills of the Zagros. Much of the Khuzestan plain is covered with marshes.
The Caspian plain is both longer and narrower. It extends for some 640 kilometres (400 mi) along the Caspian shore, but its widest point is less than 50 kilometres (31 mi), while at some places less than 2 kilometres (1.2 mi) separate the shore from the Alborz foothills. The Persian Gulf coast south of Khuzestan and the Gulf of Oman coast have no real plains because the Zagros in these areas come right down to the shore.
There are no major rivers in the country. Of the small rivers and streams, the only one that is navigable is the 830 kilometres (520 mi)-long Karun, which shallow-draft boats can negotiate from Khorramshahr to Ahvaz, a distance of about 180 kilometres (110 mi). Other major rivers include the Karkheh, spanning 700 kilometres (430 mi) and joining the Tigris; and the Zayandeh River, which is 300 kilometres (190 mi) long. Several other permanent rivers and streams also drain into the Persian Gulf, while a number of small rivers that originate in the northwestern Zagros or Alborz drain into the Caspian Sea.
On the Central Plateau, numerous rivers—most of which have dry beds for the greater part of the year—form from snow melting in the mountains during the spring and flow through permanent channels, draining eventually into salt lakes that also tend to dry up during the summer months. There is a permanent salt lake, Lake Urmia (the traditional name, also cited as Lake Urmiyeh, to which it has reverted after being called Lake Rezaiyeh under Mohammad Reza Shah), in the northwest, whose brine content is too high to support fish or most other forms of aquatic life. There are also several connected salt lakes along the Iran-Afghanistan border in the province of Baluchestan va Sistan.