The Pennyroyal Plateau or Pennyroyal Region, often spelled Pennyrile, is a large

physiographic Physical geography (also known as physiography) is one of the three main branches of geography. Physical geography is the branch of natural science which deals with the processes and patterns in the natural environment such as the atmosphere ...

region of

Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia ...

that features rolling hills,

cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

s, and

karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, Dolomite (rock), dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathe ...

topography in general. It is named for a

wild mint Wild mint may refer to: *''Mentha arvensis'' *''Mentha longifolia ''Mentha longifolia'' (also known as horse mint, fillymint or St. John's horsemint; syn. ''M. spicata'' var. ''longifolia'' L., ''M. sylvestris'' L., ''M. tomentosa'' D'Urv, ''M ...

that grows in the area. It is also called the "Mississippian Plateau," for the Mississippian geologic age in which it was formed. The Pennyroyal is bordered by the Pottsville Escarpment in the east. The Pottsville Escarpment is the transition zone from the central part of Kentucky to the higher and geologically younger

Cumberland Plateau The Cumberland Plateau is the southern part of the Appalachian Plateau in the Appalachian Mountains of the United States. It includes much of eastern Kentucky and Tennessee, and portions of northern Alabama and northwest Georgia. The terms " Al ...

in the eastern part of the state. The Pennyroyal is bordered on the north by

Muldraugh Hill Muldraugh Hill is an escarpment in Bullitt, Hardin, Jefferson, and Nelson counties of central Kentucky separating the Bluegrass on the north and north-east from the Pennyrile on the south and south-west. This escarpment fades into the Pottsvill ...

, the geological escarpment that forms the transition from the geologically older Bluegrass to the Pennyroyal. This is a series of knobs and ridges based on hard

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

s. The Pennyroyal is bordered on the west by the younger

Jackson Purchase The Jackson Purchase, also known as the Purchase Region or simply the Purchase, is a region in the U.S. state of Kentucky bounded by the Mississippi River to the west, the Ohio River to the north, and the Tennessee River to the east. Jackson's ...

. The Pennyroyal is often thought by non-geologists to include the

West Kentucky Coal Field The West Kentucky Coal Field comprises an area in the west-central and northwestern part of the state, bounded by the Dripping Springs Escarpment and the Pennyroyal Plateau and the Ohio River, but is part of the Illinois Basin that extends into ...

of Pennsylvanian age, located in the northwestern area of the state, as the southeastern part of the

Illinois Basin The Illinois Basin is a Paleozoic depositional and structural basin in the United States, centered in and underlying most of the state of Illinois, and extending into southwestern Indiana and western Kentucky. The basin is elongate, extending app ...

. The coalfield and the Pennyroyal are of different geologic ages and are separated by the Clifty Region, largely of Pennsylvanian sandstone, occasionally bituminous; the boundary with the Pennyroyal is the Dripping Springs Escarpment. To the south, the Pennyroyal continues as the

Highland Rim The Highland Rim is a geographic term for the area in Tennessee surrounding the Central Basin. Nashville is largely surrounded by higher terrain in all directions. Geologically, the Central Basin is a dome. The Highland Rim is a cuesta surro ...

Middle Tennessee Middle Tennessee is one of the three Grand Divisions of the U.S. state of Tennessee that composes roughly the central portion of the state. It is delineated according to state law as 41 of the state's 95 counties. Middle Tennessee contains the ...

. The Pennyroyal is largely in farmland where the bedrock is

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...

, and most of the Pennyroyal is based on Mississippian limestone, particularly the

St. Louis Limestone The St. Louis Limestone is a large geologic formation covering a wide area of the midwest of the United States. It is named after an exposure at St. Louis, Missouri. It consists of sedimentary limestone with scattered chert beds, including t ...

or Ste. Genevieve Limestone. In some areas, the limestone is capped with a soft sandstone. This kind of formation is featured in the

Mammoth Cave Mammoth Cave National Park is an American national park in west-central Kentucky, encompassing portions of Mammoth Cave, the longest cave system known in the world. Since the 1972 unification of Mammoth Cave with the even-longer system under F ...

area, and has enabled the formation of the world's most extensive

system. Numerous other caves exist in the Pennyroyal, where some of the most intensely cave-forming limestones of the world are to be found. Where the capping sandstone is intact, the land surface is usually forested, rugged hills.

References

{{coord, 37, 30, N, 86, 10, W, region:US-KY_scale:3000000, display=title Regions of Kentucky Plateaus of the United States Landforms of Kentucky