The Gobi is a large desert region in East Asia, covering parts of northern and northwestern China and southern Mongolia. It is a rain shadow desert, formed because the Himalayan mountain range blocks rain-carrying clouds from the Indian Ocean from reaching the Gobi. Much of the Gobi is not sandy but consists of bare rock and gravel. It is a cold desert, where it is common to see frost and occasionally snow on its dunes. Historically, the Gobi was part of the great Mongol Empire and hosted several important cities along the Silk Road. It is also a world-famous site for paleontology; the first fossilized dinosaur eggs were discovered here in the 1920s. Today, 'desertification' is a major concern as the Gobi expands rapidly into China's grasslands due to overgrazing and climate change.