The Caucasus Mountains cross it from east to west in two chains that are separated by a broad valley. The northern, or greater, Caucasus range stands between the valley and the Russian plain to the north. The southern chain, the lesser Caucasus, borders Turkey and Iran. About 50 different ethnic groups live in the Caucasus. The Caucasus Mountains are relatively young, high, and rugged.
Low mountains cross the valley between the ranges.
The northern slopes of the main range give rise to the Kuban' River, flowing to the Sea of Azov, and the Kuma and the Terek, flowing to the Caspian Sea. The Kura flows past Tbilisi to the Caspian Sea and drains most of the valley. A few high, difficult passes cross the mountains. The Ossetian and Georgian military roads cross the middle of the northern range through the Mamison Pass and Pass of the Cross. A railway loops around the east end, then runs northward along the Caspian coast.