Caspian Depression
The Caspian Depression is below sea level, consisting of large areas of marshlands in the eastern region. It is one of the largest flat lowland areas in Central Asia, covering approximately . The area is very rich in underground oil and gas reserves, and oil and natural gas pipelines cross the depression from north to south and east to west. Many geologists believe the Caspian Sea and the depression were formed by tectonic forces. Some of them also believe that the North Caspian depression became separated from the open ocean in ancient times to form an enormous salt lake. Part of the ancient Silk Road ran through this region. The two largest cities in the depression are Astrakhan in Russia and Atyrau in Kazakhstan. Today, the region is used mainly for livestock raising.