By an abandoned earthen dam, at a mountain resort 14 miles up the valley, the leaders of industry and their families created an exclusive summer retreat. But the structure of the dam was fatally flawed. On May 31, 1889, after steady spring rains, it broke without warning, and this small city in Pennsylvania was swept away in a wall of water over 30 feet high. More than two thousand people lost their lives; thousands were left homeless.