Sheltered i the Spring Mountains are remnant populations of plants and animals from a lost world when mammoths, saber-tooth lions, and giant sloths roamed the American Southwest. Surviving since the Ice Age, many of the "living fossils" are found nowhere else. Their story and that of the biological importance of the Spring Mountains is told with several ancient species of butterflies that come from a time before the desert began to form 11,000 years ago.