The Meramac Caverns have existed for the past 400 million years, slowly forming through deposits of limestone.Centuries ago, Native Americans used the cavern system for shelter. The first cave west of the Mississippi River to be explored by Europeans, it was "discovered" in 1722 by a French miner.During the 18th century, the cave was used for extracting saltpeter for the manufacture of gunpowder. In the Civil War era, the Union Army used the caves as a saltpeter plant,but the plant was discovered and destroyed by Confederate guerrillas, including future famous outlaw Jesse James. Reportedly, James and his brother and partner in crime Frank used the caves as a hideout in the 1870s. One legend claims that the sheriff sat in front of the cave, waiting for Jesse and his gang to emerge; however, they had found another exit. In 1933, the extended cave system was discovered, revealing the present 4.6 miles (7.4 km), and was introduced to the public as a tourist attraction in 1935 by Lester B. Dill, who invented the bumper sticker as a means of promoting the caverns.
The Tour of The Caves

On the 1 1/2-mile tour (8 miles of the cave have been mapped, we visited five of Meramec's seven levels.

Our guide, explained that the cave began forming when water percolating through the bedrock of the Ozark hills began to dissolve the stone and create the underground passages. Eventually the underground river carved some 18 miles of passageways and chambers, which the seeping water festooned liberally with speleothems--the stalactites (which "grow" from the ceiling) and stalagmites (which rise from the floor).

Our attention was called to a particularly unusual formation called Onyx Mountain, a haystack-like behemoth in the making for some 33 million years, that measures 28 feet high and 500 feet around at the base. Its lustrous calcite sides are striped vertically in orange (iron stains), black (manganese stains) and pure white (no stains--meaning little or no iron or manganese in the water). But whereas one side continues to enlarge, albeit at a glacial rate (75 years for a layer of stone as thick as a coat of paint), the other has grown to the ceiling, cutting off its water supply, and thus has "died."

The last stop is at the 78-million-year-old "theater," which features a "stage curtain" 70 feet high, 60 feet wide and 35 feet thick, made up of the most complex geologic forms imaginable, stone "drapery" at its finest.