Mammoth Cave near Duck Creek Village, Utah, is a sprawling, ancient underground complex on the Markagunt Plateau and one of the state's largest lava tubes. Geological Origins: Formed by cooling lava and water less than 2,000 years ago, the underground network sits at an elevation of roughly 8,050 feet. Bat Sanctuary: Portions of the cave system are gated and closed to entry every year from October 1 through April 30 to protect populations of hibernating Townsend’s big-eared bats.