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  • Writer's pictureTim Murphy

Mammoth Cave

An ethereal environment lies beneath the hills of Kentucky; a gargantuan natural phenomenon unrivaled in magnitude and sublimity. Mammoth Cave—the world’s longest cave system—has tantalized mankind’s visceral interests for centuries with its mystic permanence and renowned biodiversity. It is a truly remarkable specimen of geophysical agency that holds incredible significance in human history.

Mammoth Cave’s subterranean labyrinth emerged approximately ten million years ago when mildly-acidic groundwater began percolating through cracks in sandstone caprock and eroding substrata comprised of comparatively pervious limestone—calcium carbonate concentrations that derived from marine organisms during the Mississippian Period (359 – 323 million years ago). This sedimentary dissolution gradually intensified over millennia, creating underground tributaries that sustained the evolving Green River Basin. However, due to terrestrial weathering and cyclic glacial periods, the Green River’s water table elevation has decreased over the past five million years. Water flows consequently receded from Mammoth Cave’s upper passageways, leaving behind a convoluted complex of earthen cavitations.

Pre-Columbian peoples first discovered Mammoth Cave 4,000 – 5,000 years ago and established an extensive mineral harvesting operation within its chambers. Evaporites, such as gypsum and mirabilite, were valuable commodities in indigenous cultures. There is little surviving evidence that demonstrates how these minerals were implemented, but leading anthropologists theorize they were most likely used for medicine, trade, and ritual activities. Mining practices ceased around 200 BCE, leaving Mammoth Cave in obscurity for two thousand years.

European settlers rediscovered Mammoth Cave during the late 1790s. Local legend suggests that a young boy, John Houchins, stumbled upon the geological marvel while hunting bears; however, there is insufficient information validating this story. Mammoth Cave was first officially assessed during a 1799 geographic survey—it was registered on a two-hundred-acre land grant for Valentine Simmons, though ownership changed several times over the ensuing decade. In 1808, entrepreneurs Charles Wilkins and Fleming Gatewood purchased the property for $3,000 and organized efforts to harvest Mammoth Cave’s abundant saltpeter (potassium nitrate) deposits—a product of bat guano accumulation and key ingredient for gunpowder manufacturing.

Saltpeter miners—many of whom were enslaved African Americans—cleared the cave floor of rocks and debris, exposing the nitrate-rich “niter dirt” below. Laborers excavated two to three feet of this sedimentary material, discarded any coarse particles, and transported the remaining fine-grained silt to the Rotunda for lixiviation. Surface freshwater sluiced down fifteen-hundred-foot tulip poplar pipes and filtered through the refined niter dirt. The resulting filtrate—a calcium nitrate solution called “niter beer”—was siphoned back to the cave entrance through a gravity feed pumping system; a contemporary marvel of engineering technology.

The niter beer was subsequently mixed with hardwood ashes, which contained high concentrations of potassium hydroxide. Upon combination, white calcium hydroxide “curds” precipitated to the bottom of the agitation tank, leaving behind aqueous potassium nitrate. This fluid was combined with ox blood or alum and boiled in iron kettles—the additives interacted with organic material and other mixture impurities, forming an easily-removable scum. The tempered liquor was then strained through a cheesecloth and returned to the evaporators, allowing for needle-shaped potassium nitrate crystals to materialize. Though a labor-intensive production process, potassium nitrate was deemed superior to calcium or sodium compounds due to its hydrophobic properties.

During the War of 1812, Mammoth Cave’s saltpeter became extremely valuable. Domestic demand for gunpowder (and concomitantly saltpeter) was at an all-time high as British naval blockades prevented its importation. In August 1812, Philadelphia financier Hyman Gratz acquired Gatewood’s company shares for $10,000 and instituted industrial sophistication to the cave’s nitrate mining operation. By February 1815, Mammoth Cave had produced over 400,000 pounds of saltpeter.

Peacetime drastically reduced saltpeter demand, and consequently Mammoth Cave’s value. With meager industrial prospects, the former mining operation transitioned into a regional tourist attraction. Promoters touted the thousands of anthropological artifacts recovered from Mammoth Cave’s upper passageways, including “Fawn Hoof”—a prehistoric woman’s mummified remains.

In 1816, Nahum Ward—a wealthy Ohio businessman who observed Fawn Hoof—petitioned the American Antiquarian Society to procure and preserve the desiccated corpse in its museum holdings; however, the Antiquarians, believing the mummy was a hoax, rejected Ward’s request. The Ohioan purchased the remains himself and embarked on a traveling exposition that garnered considerable attention nationwide. Ironically, shortly after the inauguration of Ward’s eccentric enterprise, the Antiquarian Society pursued legal action for Fawn Hoof’s custodianship and emerged triumphant in 1817. The “Mammoth Cave Mummy” remained a public sensation for decades—she was displayed at the 1876 Centennial Exhibition in Philadelphia and 1893 World’s Fair in Chicago—but frequent transportation and improper storage caused her fragile condition to deteriorate. The Smithsonian Institution acquired Fawn Hoof’s remains during the late nineteenth century and retain possession to this day.

In 1838, Mammoth Cave was purchased by Franklin Gorin, who utilized enslaved African Americans as tour guides. One of these attendants, Stephen Bishop, would become one of Kentucky’s most celebrated historical figures. Stephen was born into slavery in 1821—purportedly the illegitimate son of his former master, Lowry Bishop of Barren County—and introduced to Mammoth Cave as a teenager. He quickly familiarized himself with the subterranean tunnel system and frequently explored its uncharted passageways. In October 1838, Stephen crossed the previously impassable “Bottomless Pit” and discovered several notable landmarks, including the Snowball Dining Room, River Styx, Fat Man’s Misery, and Great Relief Hall. In an age before electricity and sophisticated geonavigation technology, Stephen ventured through the unknown with just a rope and lantern. Even more remarkable, in 1842, Stephen illustrated one of Mammoth Cave’s first cartographic maps entirely from memory. His detailed diagram is still considered incredibly accurate by modern standards. Stephen was emancipated in 1856, but tragically died less than a year later. He is interred at the Old Guide’s Cemetery.

In 1839, Mammoth Cave was sold to Dr. John Croghan, an adventurous Louisville physician who believed that the cave’s constant temperature and humidity held therapeutic properties for tuberculosis patients. During the winter of 1842, Dr. Croghan operated an experimental sanatorium within Mammoth Cave’s earthen chambers. Sixteen consumptives agreed to make residence there, living in near-complete sequestration from the surface world; although, guided cave tours periodically passed through the “invalid’s village.”

Croghan’s patients initially expressed symptomatic improvements during the experiment’s early stages. With these encouraging preliminary reports, the ambitious doctor began drafting plans for a more sizeable subterranean hospital; however, as the weeks progressed, remedy depreciated into suffering. Smoke and ash accumulated within the cave’s poorly ventilated environment, causing irritation and degradation of the participants’ already-compromised lung tissue. The deleterious conditions of the cave-dwelling community startled unsuspecting sightseers. One tourist recalled “a bizarre scene [of] pale, spectral figures in dressing-gowns…slipping in an out of shadowed huts; the silence of the cave broken by hollow coughing and muttered conversations.” Of Croghan’s sixteen original patients, none were cured and five died during the experiment—their bodies laid out on ‘Corpse Rock’ until the underground sanatorium was unceremoniously shut down in early 1843. Dr. Croghan himself succumbed to tuberculosis in 1849.

During the years of Reconstruction, Mammoth Cave averaged between forty and fifty thousand annual visitors, many of whom arrived via the Louisville & Nashville Railroad at Glasgow Junction (present-day Park City). However, due to its relative remoteness, the natural attraction was only accessible by stagecoach; an inferior mode of travel when considering commuter volume. In 1874, Colonel Larkin Procter chartered the Mammoth Cave Railroad—an 8.7-mile railway spur that effectively replaced the primitive carriage roads and drastically improved transportation efficiency. Passenger service began in 1886 at the cost of three dollars per ticket. While the advent of automobiles forced the rail line’s closure in 1931, portions of this historic route can still be appreciated along the multipurpose Mammoth Cave Railroad Bike and Hike Trail.

Mammoth Cave’s commercial success stimulated rampant land speculation across southcentral Kentucky. Prospectors frantically sought stake in the region’s burgeoning tourism industry, igniting a period of bitter competition known as the “Kentucky Cave Wars.” Rival businesses regularly posted misleading advertisements along highways, intending to deceive unwary travelers from opposing attractions, while company solicitors (known as “cappers”) served as agents of destruction—sabotaging roadways, vandalizing rock formations, and burning down adversarial ticket stands.

The cave country feuding reached a feverish pitch in 1915, when petroleum entrepreneur George D. Morrison began trespassing inside Mammoth Cave. The intrusive speculator conducted illegal surveys of the cave's interior, hoping to locate its elusive “back door," but he was eventually caught and given in a lifetime ban from the attraction. Undaunted, Morrison returned in 1921, armed with a new approach. He purchased two thousand acres of land surrounding the Mammoth Cave estate and blasted dynamite into sinkholes, uncovering vertical shafts and cavernous passages below—these earthen corridors were later confirmed to be part of the Mammoth Cave system. Though artificial in configuration, Morrison’s ”New Entrance to Mammoth Cave” became an instant sensation. Tourists enjoyed spacious subterranean chambers, colorful gypsum deposits, and magnificent speleothems—including the iconic Frozen Niagara flowstone formation—all accessible from the contemporary, 25-room New Entrance Hotel.

In 1926, the trustees of Mammoth Cave filed several lawsuits against Morrison, accusing the venture capitalist of “intimidation, threats, force, violence, and other unlawful means” to lure business away from the Historic Entrance. The litigation also contained a cease-and-desist order, barring Morrison from using the name “Mammoth Cave” in any marketing materials. While the discontinuance was partially upheld—Morrison’s firm was compelled to include the phrase, "We do not show any part of the cave which prior to 1907 was generally known as Mammoth Cave, that portion of the cave can be seen only through the old entrance” in all advertising—Morrison maintained independent proprietorship of his cave access. He eventually sold the property to future national park developers in 1931 for $290,000.

Driven by similar ambitions for profit, 37-year-old William “Floyd” Collins—a local spelunker whose family owned Great Crystal and Dead Horse Caves—attempted to explore the recently-discovered Sand Cave on January 30, 1925. While trying to negotiate its narrow crevices, Collins accidentally dislodged a 27-pound boulder that crushed his left ankle, leaving him trapped sixty feet below the earth’s surface. Two good Samaritans, Jewell and Edward Estes, managed to locate Collins the following morning, but were unable to free the imperiled caver.

Reports of Collins’ entrapment quickly spread across Kentucky. Dozens of engineers, geologists, and amateur explorers descended upon Sand Cave to aid rescue efforts, while news media outlets dispatched journalists to cover the dramatic developing story. One reporter, William Burke “Skeets” Miller of the Louisville Courier-Journal, received permission from Floyd’s brother, Homer, to interview the ensnared spelunker. Being of small stature, Skeets was one of a scant few who could clamber down the confined, claustrophobic corridor. Moved by sympathy, Skeets joined the relief efforts, clearing rubble from Collins’ leg and exposing the culprit boulder. He then attempted a lengthy, but unsuccessful, attempt to pry the stone loose. Skeets Miller would later receive a Pulitzer Prize for his courageous efforts.

After 72 excruciating hours, Lieutenant Robert Burdon of the Special Police-Fire Rescue Team attempted to extricate Collins with a chest harness, but his vigorous effort failed, causing only more agony. The following day, three craftsmen from the Woodson & Kratch Monument Company of Louisville endeavored to chisel away overhanging debris inside the cave, but John Gerald—Collins' friend and caving enthusiast—emphatically rejected the idea, believing such disruption would destabilize the terrestrial passageway. Disagreements between local volunteers and "outsiders" intensified, causing pestilent delays in rescue operations. Meanwhile, Collins' condition was deteriorating. Although rescuers were able to provide food, water, and electricity, the effects of exposure were becoming progressively more difficult to mitigate.

The initial frantic and ill-conceived rescue attempts exacted their toll on the sandstone tunnel. Six days of constant activity and periodic rains eroded the cave's structural integrity—its ceiling eventually collapsed on February 4, entombing Collins in a Cimmerian hellscape.

The Kentucky Caving Crisis evoked nationwide fascination. Scores of curiosity-seekers descended upon Sand Cave, eagerly clamoring to observe the ongoing rescue efforts. The sensationalism climaxed on “Carnival Sunday” (February 8) when ten thousand spectators crowded around the extrication site, obstructing roadways and trampling farmlands in the process. Governor William J. Fields dispatched the Kentucky National Guard to contain the masses and instructed its commanding officer, Brigadier General Henry H. Denhardt, to handle all future lifesaving operations.

With Sand Cave’s entrance completely obstructed, General Denhardt ordered engineer Henry St. George Tucker Carmichael, superintendent of the Kentucky Rock Asphalt Company, to excavate a vertical shaft above Collins’ position. Carmichael assembled a select group of railroad workers, miners, and laborers from the State Highway Commission to execute the job, but intentionally excluded local townspeople from participating, which only exacerbated the preexisting social dissent.

Carmichael’s crew made quick work removing the top twenty feet of soil in less than ten hours; however, the presence of nearly-impenetrable bedrock sublayers stymied their progress to an arduous six inches per hour. Excavation efforts were further complicated on February 11, when a unremitting wintry mix inundated southern Kentucky. The heavy precipitation caused the shaft walls to slump and necessitated the installment of shoring supports.

Two weeks of nonstop rescue efforts yielded unsatisfactory results, and the once-sympathetic public grew increasingly impatient—some even began questioning the legitimacy of Collins’ predicament. Three prevailing rumors emerged out of this speculative discourse: 1) Collins’ entrapment was a colossal hoax designed to vivify Kentucky cave tourism, 2) media outlets were purposely interfering with lifesaving operations to prolong the drama, and 3) Collins had been dead this whole time. The conjecture was so pervasive that Governor Fields appointed a court of inquiry to reaffirm the situation’s harsh reality.

On February 16—after eighteen perilous days of entrapment—rescuers finally burrowed into Sand Cave, but discovered a somber sight within its earthly void. Floyd Collins was dead, having succumbed to the effects of exposure approximately 48 – 72 hours prior, according to the medical examiner. Not willing to risk additional lives for an exhumation, state officials wistfully sealed Collins’ cadaver inside Sand Cave. Two months later, Floyd’s relatives disinterred his body and reburied it underneath a stalagmite headstone in the family cemetery. Unfortunately, the deceased spelunker did not rest peacefully for very long. In 1927, Dr. Harry Thomas—a local dentist who acquired the Collins’ family landholdings—disentombed Floyd’s remains and displayed them inside a glass coffin within Great Crystal Cave. While clearly an unapologetic commercial exploit of a national tragedy, the macabre resting chamber possessed a curious magnetism that attracted thousands of visitors. Collins’ posthumous history became even more morbid on March 18, 1929, when his body was stolen from its cavernous mausoleum. Although authorities quickly recovered Floyd's remains from the Green River, his left leg was missing and has never been found. The mutilated cadaver remained in Great Crystal Cave for an additional six decades before being permanently reinterred at Mammoth Cave Baptist Church Cemetery.

The death of Floyd Collins marked a paradigm shift for the Kentucky Cave Wars. The once-rampant infighting between cave proprietors fell under considerable scrutiny from local lawmakers. Calls to transform Mammoth Cave into a national park also intensified during the tragedy’s immediate aftermath. Conservancy advocates brought their arguments before Congress, who promptly authorized the creation of Mammoth Cave National Park on May 25, 1926.

The national park’s organization was dependent on sufficient land acquisition. While some property owners willingly sold or donated their assets to the federal government, much of Mammoth Cave’s land was acquired through eminent domain, which displaced hundreds of families from their generational homesteads. Between 1933 and 1942, the Civilian Conservation Corps (CCC) razed thousands of structures in order to restore the landscape to its “natural state.”

In 1935, a team of CCC workers discovered the remains of an ancient Native American—named “Lost John”—who had been crushed underneath a fallen boulder approximately 2.5 miles inside Mammoth Cave. The mummified corpse was removed, studied by anthropologists, and displayed on the Historic Tour route for several decades. During the 1970s, as sentiments towards grave desecration became more empathetic for the deceased, Lost John was removed from public view. He currently rests in an undisclosed location within Mammoth Cave.

In 1938, Dr. Nathaniel Kleitman, a psychologist from the University of Chicago, and his graduate student, Bruce Richardson, performed a sleep cycle experiment within Mammoth Cave. Both men resided underground for 32 days, sequestered from the alteration of day and night. They adapted a 28-hour schedule—nine hours of sleep, ten hours of work, and nine hours of leisure—and recorded their body temperatures throughout the trial. Kleitman and Richardson’s research provided groundbreaking evidence supporting the presence of internal mechanisms that regulate circadian rhythms and 24-hour temperature cycles, even in the absence of external cues. Kleitman published an account on the Mammoth Cave study in his 1939 scholarly publication Sleep and Wakefulness

On September 9, 1972, a team of spelunkers exploring the adjacent Flint Ridge Cave system—believed to be the world’s longest with 86.5 miles mapped—discovered a subterranean passage into Mammoth Cave. This monumental connection, known as the “Mount Everest of Speleology," combined the two previously-distinct subterranes into a sprawling 144.4-mile network (the name ‘Mammoth Cave’ was retained due to its popularity). Today, Mammoth Cave is currently charted at 426 miles, but some geologists believe there could still be nearly two hundred miles left undiscovered.


With hundreds of miles to explore, Mammoth Cave offers a multitude of tour options suitable for every skillset, from leisurely walks to cave crawling expeditions. This article will discuss three more popular experiences, the first being the Extended Historic Tour. The journey begins at the Historic Entrance—an imposing natural gateway into the underworld. A gust of barometric wind greets visitors as they pass through Houchin’s Narrows and enter the grandiose Rotunda. This magnificent chamber (a quarter-acre in size) features several leaching contraptions from Mammoth Cave’s early saltpeter operation and two memorials commemorating Kentucky’s fallen during World War I—the American Legion (c. 1922) and American War Mothers (c. 1929) monuments.

The guided tour continues down Broadway (the main cave passage lined with rubble and centuries-old cedar pipes) and pauses at Methodist Church—the location where Reverend George Slaughter Gatewood held religious services during the 1830s. Visitors venture another 0.4 miles inward before encountering two stone tuberculosis huts, relatively undisturbed since Dr. Croghan’s failed sanatorium experiment in 1843.

From the tuberculosis huts, the tour reverses direction and descends down Black Snake Avenue—a winding, paved trail lined with historic smoke signatures from visitors’ past. The path plunges deeper into Mammoth Cave’s depths and crosses over two vertical shafts: “Bottomless” Pit and Side Saddle Pit. Hikers must squeeze through the contorted narrows of Fat Man’s Misery—which one visitor described as “a torturous rift, a snake in convolution, and an avenue of torture in ruggedness, narrowness, and lowness [that] would perplex a groundhog”—before being able to stand upright in Great Relief Hall.

Guests may briefly rest up in River Hall (283 feet below the surface) before tackling the 190-foot ascent of Mammoth Dome. The trail links with Audubon Avenue—a large upper cave passage that once housed the briefly operational Mammoth Cave Mushroom Company between 1881 and 1882—which reconnects to the Rotunda. The Extended Historic Tour covers approximately two miles underground, features 540 stairs, and takes 2.25 hours to complete. It is an immersive experience that accentuates the long-standing fascination associated with Mammoth Cave.

Trail Rating: 10/10

The second tour option explores Gothic Avenue, which begins much like the Extended Historic Tour, but deviates past the Methodist Church. Instead of continuing down Broadway towards the tuberculosis huts, visitors are directed onto a metal walkway that crosses over several saltpeter vats and ascends to Booth’s Amphitheater—named after Shakespearean actor Edwin Booth (brother of the infamous John Wilkes Booth) who visited Mammoth Cave in 1876. This chamber marks the beginning of Gothic Avenue; a passageway adorned with smoke signatures and pyramidal stone stacks created by visitors during the nineteenth and early twentieth centuries.

The tour route passes by several speleothem formations, including the Bridal Altar, which features three large dripstone columns. Several couples have been wed there, though matrimonial ceremonies are no longer permitted under NPS jurisdiction. Gothic Avenue terminates at Lover’s Leap—a slender-pointed rock slab hanging ominously above a deep vertical shaft. The Gothic Avenue Tour is a shorter experience compared to its Extended History counterpart (covering 1.7 miles in two hours) but contains intriguing details concerning early American tourism, perfect for any history enthusiast. Trail Rating: 9/10

The final subterranean experience is the Grand Avenue Tour. This route distinguishes itself from the previous two for several reasons. First, Grand Avenue focuses more on Mammoth Cave’s geological features rather than its human history. Second, instead of walking from the Visitor Center to the Historic Entrance, participants are shuttled to a secondary entrance roughly two miles away. Finally, this is longest and most strenuous walking tour currently available, covering four miles and over fifteen hundred stairs in four hours.

The Grand Avenue Tour involves numerous inclines, tubular passageways, and narrow slot canyons. The majority of this section is “dry” (meaning few speleothems) but visitors have an opportunity to view the Frozen Niagara flowstone near the end of the experience. This tour provides a good workout, but there really is not much to see along the way, which makes four hours underground seem like an eternity. Consider alternative experiences—such as the Frozen Niagara or Domes & Dripstones tours—which are less strenuous, less time-consuming, and feature more fascinating rock formations. Trail Rating: 5/10

Mammoth Cave amalgamates natural wonder with human fascination. The seemingly endless subterranean landscape provides an enigmatic environment that stimulates innate desires for exploration and adventure. These thrilling ambitions are further stimulated throughout the eponymic national park, which features numerous campsites, waterways, and eighty-five miles of recreational trails across its 52,830 acres.

Learn more about Mammoth Cave National Park by visiting the National Park Service, Parkaction, Trail and Hitch, and More Than Just Parks

For more on the Mammoth Cave Mummies, check out NPS, Only in Your State, and Early Marietta

Learn more about Stephen Bishop in Smithsonian Magazine and Unique Coloring

Check out Atlas Obscura, Smithsonian Magazine, Haunted Palace Blog, and The Darker Side of Life Podcast for more about tuberculosis and Dr. Croghan's Mammoth Cave Sanatorium

Visit Kentucky Cave Wars and the National Register of Historic Places to learn more about the Mammoth Cave Railroad

Learn more about the Mammoth Cave Sleep Experiment at UChicago and Story Maps

Read the following publications for more historical information:

  1. Bridwell, Margaret M. The Story of Mammoth Cave National Park, Kentucky: A Brief History. (1959).

  2. Crothers, George M., Christina A. Pappas, and Christian D. Mittendorf. "The History and Conservation of Saltpeter Works in Mammoth Cave, Kentucky." (2013).

  3. Eke, Collins U. "Where Did They Go? Analysis of Out-Migration from Mammoth Cave National Park, 1920-1940." (2019).

  4. Hill, Carol A., and Duane DePaepe. “Saltpeter Mining in Kentucky Caves.” The Register of the Kentucky Historical Society 77, no. 4 (1979): 247–62.

  5. O'Dell, Gary A. "The Celebrated Black Explorer Stephen Bishop and Mammoth Cave: Observations by an English Journalist in 1853." (2018).

  6. Sulzer, Elmer G. “The Mammoth Cave Railroad.” The Railway and Locomotive Historical Society Bulletin, no. 99 (1958): 31–41.


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