An Afar camel caravan crosses the salt flats of Lake Assal, Djibouti, as shadows lengthen in the late afternoon sun. At 509 feet below sea level, Lake Assal is the lowest place in Africa. Extremely high midday temperatures, which can surpass 120 Fahrenheit, force the Afar to arrive in the late afternoon and immediately set about collecting salt from deposits that are at least 109 feet thick. Each camel carries between four and ten thirty-pound sacks according to its size and maturity.The caravans leave again before daybreak the following day. The salt is sold across the border in Ethiopia.