Great Salt Lake is the remnant of ancient Lake Bonneville, as shown by visible shorelines along the east mountains and Antelope Island. Lake Bonneville existed from about 14,000 to 32,000 years ago, covered 20,000 square miles of Utah, eastern Nevada, and southern Idaho, and was over 1,000 feet deep. Its shoreline terraces include the Provo terrace at 4,840 feet above sea level and the Bonneville terrace at 5,220 feet. Mysteries once associated with this salty body of water included ideas that it connected to the Pacific Ocean and stories of a lake monster, a huge whirlpool, and a submarine village. Amid such speculation, Captain Howard Stansbury's 1849 map scientifically defined the lake's shoreline and river tributaries accurately. Great Salt Lake is salty because it has no outlet; water flows in from the mountains and evaporates, leaving behind minerals including salt, which several commercial companies around the lake harvest. The lake has an elevation of 4,200 feet above sea level, is 75 miles long and 30 miles wide, covers 2,000 square miles, has a greatest depth of 34-40 feet and a mean depth of 13 feet, and has an approximate shoreline of 200 miles. Its historic low was 4,193 feet in 1963, and its historic high was 4,212 feet in 1873, 1986, and 1987.