At 509 feet below sea level, Lake Assal is the lowest place in Africa. Thousands of years ago, the lake level was much higher as evidenced by the watermark on the hills. Nomadic Afar tribesmen come here with their camels to collect salt. Extremely high midday temperatures, which can surpass 120 Fahrenheit, force them to arrive in the late afternoon and immediately set about collecting salt from deposits that are at least 109 feet thick. The camel caravans leave again before daybreak the following day. Each animal carries between four and ten thirty-pound sacks according to its size and maturity. The salt is sold across the border in Ethiopia.