File:Hidden River Cave (Horse Cave, Kentucky, USA) 2.jpg

English: Limestones in the Mississippian of Kentucky, USA.

This sinkhole in the town of Horse Cave, Kentucky bottoms out at the entrance to Hidden River Cave, which has about 11.5 miles of mapped passages. The beds along the walls of the sinkhole and in the cave itself are Middle Missippian rocks of the St. Louis Limestone. Lithologies in the unit include limestone, chert, and shale. An actively flowing stream is in the cave, as are three impressive breakout domes, the largest of which is "Sunset Dome".

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From signage in visitor center:

In 1916, a half mile-long section of Horse Cave was opened to the public for tours. As part of a promotion, Doctor H.B. Thomas ran a local contest to rename the cave, and the name "Hidden River Cave" was chosen for tourist use. Hidden River boasted elegant galleries and for a short time offered scenic boat rides along the river's winding course through the cave. "Sunset Dome", at the end of the tour, is a room approximately 250 feet in diameter and 100 feet tall. The cave, which has yet to be fully explored, was home to a number of rare cave creatures, including a large population of blind cavefish and blind cave crayfish.

For several decades, the grossly contaminated Hidden River Cave lay neglected and shunned by humans. The cave streams were void of life, except for strings of sewage bacteria and writhing bloodworms that thrived in the nearly oxygen-free underground water. Gone were the once-plentiful blind cavefish that, like most animals adapted to living in cave streams, require highly stable conditions. The entrance to the cave was nearly invisible to passersby, surrounded by buildings, thick vegetation, and a high fence. It was easy to ignore the cave, except each summer when the horrible stench of raw sewage belched from its mouth and reminded everyone of its presence.

In December 1989, sewage stopped flowing into the cave, thanks to new state-of-the-art sewage treatment systems built for the communities of Horse Cave and Cave City. Treated sewage from these two plants now enters a carefully studied and designed conveyance line that transports the wastewaters to an appropriate disposal site which will not damage groundwater supplies. This was part of a state and federally funded project costing many millions of dollars to restore the groundwater quality of the whole region. The terrible odors soon were gone and the cave stream was on its way to naturally restoring itself.

By the summer of 1991, the underground river had taken on enough oxygen to once again support indigenous life. Numerous crayfish had migrated to previously polluted sections to feast on dying sewage organisms. As the process of recovery continues and conditions begin to stabilize, more native cave animals will once again colonize the passageways.

In 1992, cleanup efforts in the large sinkhole entrance to the cave began to restore the lush setting described by John Muir after his 1867 visit. Exploration and mapping of the cave also resumed under the leadership of the American Cave Conservation Association after a 50-year hiatus. The full extent of the passageways is still unknown. In addition, plans to reopen the cave to the public were considered. The first stage was accomplished in 1992 by improving the steps and walkway to the underground river.

Establishment of the American Caves and Karst Center in 1992 at the mouth of Hidden River Cave has once again called attention to this remarkable natural feature: remarkable for its unique setting, its inherent beauty, its quintessential geology, and the successful rejuvenation of its underground river system. This is truly a classic groundwater success story.

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John Muir's visit in 1867 Thousand Mile Walk to the Gulf

The entrance (to Horse Cave) seems like a noble gateway to the birthplace of springs and fountains and the dark treasuries of the mineral kingdom. This cave is in a village (of the same name) which it supplies with an abundance of cold water, and cold air that issues from its fern-clad lips. In hot weather crowds of people sit about it in the shade of the trees that guard it. This magnificent fan is capable of cooling everybody in the town at once.

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Stratigraphy: Horse Cave Member, upper St. Louis Limestone, Middle Mississippian

Locality: entrance to Hidden River Cave, town of Horse Cave, southern Kentucky, USA (37° 10' 45.51" North latitude, 85° 54' 22.38" West longitude)