in west-central Kentucky, U.S., area of numerous sinkholes and caves in the Pennyrile (or Pennyroyal) region. The area includes the interconnected caves of Mammoth Cave National Park and Flint Ridge Cave System. Abundant surface and underground water together with limestones deposited during the Early Carboniferous (Carboniferous Period) Epoch (360 to 320 million years ago) have combined to create a vast network of underworld caverns, rivers, and lakes. The caves include extensive sulfate mineral formations, stalactites, and stalagmites (stalactite and stalagmite).