Tourists on South Dakota's Interstate 90 may soon visit more than just Mount Rushmore, Prairie Dog Town and the world's largest drugstore, Wall Drug. Some of the nation's 1,000 Minuteman missile silos are ripe for historic preservation, says the National Park Service, which is looking at two launch sites adjacent to Badlands National Park. The Defense Department boasted in 1962 that the Minuteman - America's first "push-button nuclear missile' - could reach Soviet targets in under 30 minutes. When the Soviet Union collapsed and the Cold War ended, says Park Service staffer Gregory Kendrick, missiles were quickly dismantled. Now, "we're afraid of losing something of significance," he says. The Park Service is considering two silos for preservation, Delta sites one and nine, because they are on easily transferable Forest Service land and sit close to the popular I-90 corridor. If they are designated historic sites, visitors will feel they are viewing a "day-in-the-life of a Minuteman missileer," says a Park Service study. During alert status, two-man crews sat underground, strapped into chairs in blast-proof launch centers, awaiting commands from the president. Management alternatives for the two silos include destroying them, hiring a private company to preserve the sites, or designating them as National Historic Sites. To receive a copy of the Minuteman Special Resource Study, contact Gregory Kendrick, National Park Service, P.O. Box 25287, Denver, CO 80225-0287 (303/969-2875).