Mammoth Cave National Park

Kentucky · Established July 1, 1941

The longest known cave on Earth, under a quiet Kentucky forest

Area: 72,473 acres
Established: July 1, 1941
Recreation visits: 660,734 / yr
State: Kentucky
Surveyed cave length: More than 426 mi (686 km), the longest known cave system in the world
Cave temperature: About 54°F (12°C) year-round deep in the cave

Mammoth Cave Weather Forecast

Loading the National Weather Service forecast for Mammoth Cave…

Seven-day outlook at the park's reference point (37.198, -86.131). Elevation changes everything in the mountains — expect colder, windier and wetter conditions on high ground.

Map of Mammoth Cave National Park

The Park

Beneath the wooded ridges of south-central Kentucky lies the longest known cave system in the world, a labyrinth of more than 426 surveyed miles of passages stacked in levels like the floors of a buried city. Mammoth Cave has drawn explorers, miners, guides, and scientists for centuries, and every year surveyors add new miles to the map.

Established as a national park on July 1, 1941, Mammoth Cave is also a World Heritage Site and the core of an International Biosphere Reserve. Its surface is a gentle country of oak and hickory forest, sinkholes, and springs, cut by the slow green loops of the Green River, while below ground live eyeless fish, cave-adapted crickets and beetles, and colonies of endangered bats.

Geography

The park covers about 72,500 acres in Edmonson, Hart, and Barren counties, on the edge of the Chester Upland where a resistant sandstone cap overlies thick limestone. To the south and east lies the Pennyroyal Plateau, a sinkhole plain pocked by thousands of depressions that funnel rainwater underground. Within the park, flat-topped ridges such as Mammoth Cave Ridge, Flint Ridge, and Joppa Ridge stand above deep, forested hollows.

The Green River winds east to west through the park and is joined by the Nolin River at its western end. The river is the master drain of the cave system: underground streams such as the Echo River and River Styx emerge from springs along its banks, and the water level in the lowest cave passages rises and falls with the river. Above ground, many valleys hold no surface streams at all, because water sinks directly into the karst.

Landmarks

Historic EntranceCaveThe natural sinkhole entrance used for thousands of years and still the gateway for many cave tours.
River Styx SpringRiverA cave river emerges into daylight here and flows a short distance into the Green River.
Echo River SpringRiverWater from one of the cave's underground rivers wells up in a quiet blue pool near the Green River.
Green River FerryRiverA small cable-guided ferry that carries cars across the Green River south of the visitor center.
Turnhole BendRiverA tight loop of the Green River fed by a large spring that drains much of the sinkhole plain.
Cedar SinkValleyA huge collapse sinkhole where a stream rises from the ground, flows across the floor, and vanishes again.
Sloans Crossing PondLakeA small sinkhole pond perched on the sandstone caprock, rich in frogs, turtles, and dragonflies.
Great Onyx CaveCaveA historic show cave on Flint Ridge known for its gypsum and dripstone formations.
Nolin RiverRiverA tributary that joins the Green River at the park's western end.

Geology

The story of Mammoth Cave begins in a warm, shallow sea that covered the interior of North America during the Mississippian Period, roughly 360 to 320 million years ago. Countless shells and skeletons of marine creatures piled up on the seafloor and hardened into hundreds of feet of limestone, including the St. Louis, Ste. Genevieve, and Girkin formations. Near the end of that time, rivers built deltas across the region and spread a layer of sand that became the Big Clifty Sandstone.

That sandstone is the key to the cave's great size. Resistant to dissolving, it forms a protective cap over the ridges, sheltering the limestone below from collapse while still letting water seep in along cracks and at the caprock's edges. Rainwater picks up carbon dioxide from the air and soil, becoming a weak acid that slowly dissolves limestone along joints and bedding planes. Over time these tiny openings grew into tubes, canyons, and vast avenues.

The cave's layered architecture was set by the Green River. Passages began forming roughly 10 to 15 million years ago, with water flowing toward the river at whatever level it then occupied. As the river cut downward in stages, water abandoned upper passages and carved new ones below. Ice age changes in regional drainage altered the flow of water and accelerated the downcutting, leaving four dry fossil levels above the active river level. Beneath the sinkhole plain, the process continues today.

Deep time

About 360 to 320 million years agoShallow Mississippian seas deposit the thick limestones that host the cave.
Late MississippianRiver deltas spread sand that becomes the Big Clifty Sandstone caprock.
About 10 to 15 million years agoWater flowing toward the Green River begins dissolving the first cave passages.
Until about 2 million years agoThe upper levels of the cave develop while the river stands at higher elevations.
PleistoceneIce age changes in drainage speed the Green River's downcutting, and lower passage levels form.
September 9, 1972Explorers connect the Flint Ridge cave system to Mammoth Cave, creating the world's longest known cave.

The rocks

St. Louis LimestoneMississippian
The lowest of the major cave-forming limestones, notable for its abundant chert nodules.
Ste. Genevieve LimestoneMississippian
A pure limestone in which many of the largest passages are developed.
Girkin FormationLate Mississippian
Limestone with thin shale beds forming the upper cave levels beneath the caprock.
Big Clifty SandstoneLate Mississippian
The resistant sandstone caprock that protects the cave-bearing ridges.
Travertine and gypsum speleothemsQuaternary to present
Flowstone, stalactites, and gypsum flowers deposited by mineral-laden water, as at Frozen Niagara.

Trees, Plants & Ecosystems

1,327vascular plant species recorded

Cave ecosystemUnderground
A world of constant darkness and a steady 54°F, home to eyeless cavefish, cave crickets, beetles, and wintering bats.
Oak-hickory forestRidges and dry slopes
White oak, hickories, and sassafras cover the uplands, with dogwood and redbud blooming in the understory.
Mixed mesophytic hollowsMoist ravines
Tulip-poplar, beech, sugar maple, and hemlock shade rich wildflower slopes.
Green River corridorFloodplain
Sycamore and silver maple line a river with one of the most diverse fish and freshwater mussel faunas in North America.
Barrens and prairie remnantsScattered uplands
Fire-maintained openings with little bluestem, coneflowers, and rosinweeds, a remnant of the historic Kentucky barrens.

Trees

Tulip-poplarLiriodendron tulipiferaTall, straight trees of moist coves with tulip-shaped flowers.
White oakQuercus albaA long-lived oak dominating upland forests.
Shagbark hickoryCarya ovataKnown for its long, peeling strips of bark.
American beechFagus grandifoliaSmooth gray trunks in shaded ravines.
Sugar mapleAcer saccharumBrilliant orange in autumn.
Eastern hemlockTsuga canadensisA cool-climate conifer that survives in shaded sandstone gorges.
American sycamorePlatanus occidentalisWhite-limbed giants of the Green River banks.
BlackgumNyssa sylvaticaAmong the first trees to turn scarlet in fall.
Eastern redcedarJuniperus virginianaGrows on thin, rocky soils over limestone.
Flowering dogwoodCornus floridaWhite blossoms light the understory in April.
Eastern redbudCercis canadensisPink-purple flowers on bare branches in early spring.
PawpawAsimina trilobaA small understory tree with North America's largest native fruit.

Wildflowers, shrubs & other plants

BloodrootSanguinaria canadensisWhite flowers that open on sunny March days.
Virginia bluebellsMertensia virginicaNodding blue bells carpeting moist floodplains in spring.
Prairie trilliumTrillium recurvatumA maroon trillium with mottled leaves.
MayapplePodophyllum peltatumUmbrella-like leaves forming colonies on the forest floor.
Dutchman's breechesDicentra cucullariaTiny white flowers shaped like upside-down pantaloons.
Wild blue phloxPhlox divaricataPale blue blossoms in rich spring woods.
Spring beautyClaytonia virginicaPink-striped flowers among the first to bloom.
Giant caneArundinaria giganteaNorth America's native bamboo, forming canebrakes along the river.
Little bluestemSchizachyrium scopariumA prairie grass that turns copper in autumn in the barrens.
Pale purple coneflowerEchinacea pallidaDrooping pink petals in restored barrens.
Prairie rosinweedSilphium terebinthinaceumTall yellow flowers above huge basal leaves.
Cardinal flowerLobelia cardinalisRed spikes along streams, pollinated by hummingbirds.
Mountain laurelKalmia latifoliaAn evergreen shrub on sandstone bluffs.
Northern maidenhair fernAdiantum pedatumDelicate fronds on moist limestone slopes.

Wildlife

50mammals
160birds
32reptiles
27amphibians
87fish

Mammals

White-tailed deerOdocoileus virginianusVery common along park roads and fields.
Gray batMyotis grisescensAn endangered cave bat that roosts in large colonies in warm cave passages.
Indiana batMyotis sodalisAn endangered bat that hibernates in cold cave chambers.
Rafinesque's big-eared batCorynorhinus rafinesquiiA bat with enormous ears that roosts in caves and hollow trees.
Big brown batEptesicus fuscusA hardy bat often seen at dusk.
Tricolored batPerimyotis subflavusA small bat hard hit by white-nose syndrome.
Allegheny woodratNeotoma magisterNests in cave entrances and rocky bluffs.
North American river otterLontra canadensisSeen along the Green and Nolin rivers.
American beaverCastor canadensisActive along the Green River and its backwaters.
BobcatLynx rufusA secretive cat of forest edges.
Gray foxUrocyon cinereoargenteusA tree-climbing fox of dense woods.
RaccoonProcyon lotorSometimes wanders into cave entrances in search of food.
Eastern chipmunkTamias striatusCommon along trails and rocky slopes.
Virginia opossumDidelphis virginianaNorth America's only marsupial.

Birds

Wild turkeyMeleagris gallopavoFlocks frequently seen in fields and along roads.
Pileated woodpeckerDryocopus pileatusA crow-sized woodpecker of mature forest.
Prothonotary warblerProtonotaria citreaA golden warbler nesting in cavities over the Green River.
Wood thrushHylocichla mustelinaIts fluting song echoes through summer hollows.
Scarlet tanagerPiranga olivaceaA brilliant red bird of the forest canopy.
Worm-eating warblerHelmitheros vermivorumNests on steep, leafy slopes.
OvenbirdSeiurus aurocapillaA ground-nesting warbler with a loud teacher-teacher song.
Barred owlStrix variaIts who-cooks-for-you call rings through river bottoms.
Eastern screech-owlMegascops asioA small owl with a whinnying call.
Eastern whip-poor-willCaprimulgus vociferusCalls its name on warm summer nights.
Bald eagleHaliaeetus leucocephalusSeen along the Green River, especially in winter.
Great blue heronArdea herodiasStalks the river shallows.
Wood duckAix sponsaNests in tree cavities near water.
Indigo buntingPasserina cyaneaA vivid blue songbird of fields and edges.

Reptiles & amphibians

Cave salamanderEurycea lucifugaAn orange, black-spotted salamander of cave entrances and twilight zones.
Long-tailed salamanderEurycea longicaudaFound near springs, seeps, and cave mouths.
Northern slimy salamanderPlethodon glutinosusSticky skin secretions deter predators.
Spotted salamanderAmbystoma maculatumMigrates to sinkhole ponds on rainy late-winter nights.
Spring peeperPseudacris cruciferIts chorus announces spring at park ponds.
Timber rattlesnakeCrotalus horridusA venomous but reclusive snake of rocky, wooded hillsides.
CopperheadAgkistrodon contortrixThe park's most frequently seen venomous snake.
Eastern box turtleTerrapene carolinaA long-lived land turtle often seen after rains.

Fish

Northern cavefishAmblyopsis spelaeaA blind, pigmentless fish of the cave's underground rivers.
Southern cavefishTyphlichthys subterraneusA small eyeless fish that senses prey through touch-sensitive ridges.
Spring cavefishForbesichthys agassiziiHas small eyes and lives in springs and cave edges.
Smallmouth bassMicropterus dolomieuA popular sport fish of the Green River.
MuskellungeEsox masquinongyA large predatory fish of the Green River.
Kentucky snubnose darterEtheostoma rafinesqueiA colorful darter found only in the Green River region of Kentucky.
MooneyeHiodon tergisusA silvery river fish with large eyes.
Freshwater drumAplodinotus grunniensMakes grunting sounds using its swim bladder.

Insects & other invertebrates

Karst needleflyLeuctra schusteriA small stonefly associated with springs and karst streams.
DragonhunterHagenius brevistylusA large dragonfly that preys on other dragonflies along the river.
Gray petaltailTachopteryx thoreyiAn ancient lineage of dragonfly that breeds in forest seeps.
Ebony jewelwingCalopteryx maculataA black-winged damselfly of shady streams.
Eastern snowflyAllocapnia rectaA winter stonefly that emerges on snow and cold streamsides.

Species totals are the park's certified NPSpecies checklist (occurrence: present).

Climate & When to Visit

Mammoth Cave has two climates, one above ground and one below. On the surface, south-central Kentucky has a humid, temperate climate with warm, muggy summers and variable winters. Summer highs average in the upper 80s °F and winter highs in the low 40s. The region receives about 50 inches of precipitation a year, the most in Kentucky, with spring the wettest season. Storms occur year-round and can bring tornadoes, damaging winds, and floods in low areas, though severe weather is uncommon.

Deep inside the cave, the temperature stays near 54°F (12°C) in every season, and humidity is high. Near entrances, however, the cave breathes with the weather: in winter, cold, dense air flows in and can chill passages near the entrance, while in summer, cool cave air flows out, creating a natural breeze at the doorway. Heavy rains swell the Green River and can flood the lowest cave passages and delay some tours.

Spring
The wettest season, with wildflowers from March through May and occasional strong thunderstorms.
Summer
Hot and humid, with highs in the upper 80s °F; the cave's cool air is a welcome refuge.
Autumn
Mild, drier days and colorful foliage in October make it a pleasant time to hike and paddle.
Winter
Generally mild, with occasional snow and ice storms; fewer visitors and some reduced services.

Weather hazards

Flooding: Heavy rain can quickly raise the Green River and flood low-lying roads, trails, and lower cave passages.
Severe storms: Watch the forecast for thunderstorms and tornado warnings, especially in spring.
Heat and humidity: Carry water on surface trails in summer, as heat index values can be high.
Cave conditions: Bring a light jacket for 54°F cave air and sturdy shoes for wet, uneven passages.
Winter ice: Ice can make park roads and steep trails slick after winter storms.

Mammoth Cave Questions

When is the best time to visit Mammoth Cave National Park?

Cave tours run year-round because the cave stays near 54°F. Spring brings wildflowers and autumn offers mild weather and fall color, while summer is busiest and tours often sell out.

How long is Mammoth Cave?

More than 426 miles of passages have been surveyed, making it the longest known cave system in the world. Explorers continue to discover and map new passages.

What is the temperature inside Mammoth Cave?

Deep in the cave, the temperature is about 54°F year-round. Areas near entrances can be colder in winter or breezier in summer as air moves in and out.

How did Mammoth Cave form?

Slightly acidic water dissolved thick Mississippian limestone over millions of years, while a sandstone caprock protected the ridges from collapse. The Green River's stepwise downcutting created the cave's multiple levels.

What animals live in the cave?

The cave hosts species adapted to total darkness, including eyeless cavefish, cave crickets, and cave beetles, along with the endangered Kentucky cave shrimp. Several species of bats, including the endangered gray and Indiana bats, also use the cave.

Can you see wildlife above ground?

Yes. White-tailed deer and wild turkeys are common, and paddlers on the Green River may see herons, river otters, and bald eagles. Spring and summer bring warblers and other songbirds.

More parks in the East

← Lassen Volcanic National Park Mesa Verde National Park →

Sources: www.nps.gov · www.nps.gov · www.nps.gov · en.wikipedia.org · www.usgs.gov · irmaservices.nps.gov · Official NPS site