One of the longest rivers of the country, Zavkhan River flows from the western slope of Hangai range. It flows across mountain, steppe and the extensive Mongol Els sand dunes for over 800 kilometers and feeds Airag Lake in the Depression of Great Lakes. Mongol Els, which is one of the largest sand stretches of Mongolia covers an area 2,724 square kilometers. The sand dunes of Mongol Els are relatively vegetated and home to Mongolian and black-tailed gazelles.