The Ancient Depths

Did you know that many of the lands that now make up America’s national parks were once completely underwater? More than 100 million years ago, a giant inland sea divided North America into two smaller landmasses. This sea stretched from the Gulf of Mexico all the way to Montana! Even though much of the American West is dry desert today, its character was shaped by the many years it spent under water. From Mammoth Cave National Park in Kentucky to Glacier National Park in Montana, visit your national parks to learn how ancient seas created some of the national parks we love so much today.

Map of the United States showing all units of the National Park System

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Last updated: February 25, 2019