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Lilburn Cave, Sequoia National Park, California
Credit: Dave Bunnell/Under Earth Images/www.underearth.us.
Stashed away in Sequoia National Park are over 240 caves with maybe hundreds more undiscovered. One of the most amazing is Lilburn Cave, a marble labyrinth and California's deepest cave at over 20 miles (32 kilometers). More than 30 different kinds of minerals are found here, creating colorful and unusual cave formations.
The cave is filled with beautiful marble banding, several large streams and is "probably the most amazing in the U.S.," said cave expert R. Scott House of the Cave Research Foundation. Lilburn is not heavily decorated with speleothems the cave formations such as stalagmites and stalactites but its few formation areas are exceptional.