The highest mountain is 3415 m, and is the "Emi Koussi" in Chad. Some mountain peaks in the Sahara Desert have snow even in the summer. The main mountain ranges is the Atlas Mountains in Algeria. The Sahara's lowest point lies in the Qattara Depression in Egypt, at about 130 metres below sea level. Sand sheets and dunes are about 25% of the Sahara. The other parts are mountains, steppes with a lot of stones, and oases.