Most of the land area consists of a plateau some 1,200 m (4,000 ft) above sea level and strewn with mountains. The Zagros and Elburz ranges stamp a "V" upon the plateau; the apex is in the northwest, and within the lower area between the arms are to be found salt flats and barren deserts. Most of the drainage is from these two great ranges into the interior deserts, with limited drainage into the Caspian Sea and the Persian Gulf. The ranges run in parallel files, enclosing long valleys that provide most of the agricultural land. Mt. Damavand, northeast of Tehran, rises to 5,671 m (18,606 ft), while the Caspian littoral is below sea level and has a semitropical climate. Only the Karun River, emptying into the Persian Gulf, is navigable for any distance, but the rivers that rush down from high altitudes offer fine sources of power.
Harbors of limited depth are found along the Persian Gulf, and the Caspian Sea has similar facilities for coastal fishing and trade. Iran is geologically unstable with occasional severe earthquakes. About 140,000 people were killed in Iranian earthquakes during the twentieth century.