List of mapped rock formations in Pennsylvania

The following is a list of the mapped bedrock units in Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...

. The rocks are listed in stratigraphic order.

System	Group name	Formation name	Member name	Map symbol
Triassic Triassic The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...	Newark Group Newark Group The Newark Group, also known as the Newark Supergroup, is an assemblage of Late Triassic and Early Jurassic sedimentary rocks which outcrop intermittently along the United States East Coast; the exposures extend from Massachusetts to North Carolina, with more still in Nova Scotia...	Passaic Formation Passaic Formation The Passaic Formation is a mapped bedrock unit in Pennsylvania, New Jersey, and New York. It was previously known as the Brunswick Formation since it was first described in the vicinity of New Brunswick, New Jersey. It is now named for the city of Passaic, New Jersey, which is near where its type...		Trp
Triassic	Newark Group	Lockatong Formation Lockatong Formation The Triassic Lockatong Formation is a mapped bedrock unit in Pennsylvania, New Jersey, and New York. It is named after the Lockatong Creek in Hunterdon County, New Jersey.-Description:...		Trl
Triassic	Newark Group	Stockton Formation Stockton Formation The Triassic Stockton Formation is a mapped bedrock unit in Pennsylvania, New Jersey, and New York. It is named after Stockton, New Jersey, where it was first described...		Trs
Permian Permian The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...	Dunkard Group Dunkard Group The Permian Dunkard Group is an area of rock, Early Permian in age, in the south of Ohio, southwestern Pennsylvania, West Virginia and the hilltops of the Georges Creek Basin of Maryland. It is found primarily in Washington County. It is notable for being one of the few areas of Permian sediment...	Greene Formation		Pg
Permian	Dunkard Group	Washington Formation		Pw
Pennsylvanian Pennsylvanian The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...	Conemaugh Group	Cassleman Formation		φcc
Pennsylvanian	Conemaugh Group	Glenshaw Formation Glenshaw Formation The Glenshaw Formation is a mapped sedimentary bedrock unit in Pennsylvania, Maryland, West Virginia, and Ohio, of Pennsylvanian age. It is the lower of two formations in the Conemaugh Group, the upper being the Casselman Formation. The boundary between these two units is the top of the marine...		φcg
Pennsylvanian		Allegheny Formation Allegheny Formation The Pennsylvanian Allegheny Formation is a mapped bedrock unit in western and central Pennsylvania, western Maryland and West Virginia, and southeastern Ohio...		φa
Pennsylvanian		Llewellyn Formation Llewellyn Formation The Llewellyn Formation is a mapped bedrock unit in eastern Pennsylvania. It was previously known as the "coal measures" and the post-Pottsville rocks. The formation is named for the community of Llewellyn in Schuylkill County.-Description:...		φl
Pennsylvanian		Pottsville Formation Pottsville Formation The Pennsylvanian Pottsville Formation is a mapped bedrock unit in Pennsylvania, western Maryland, West Virginia, and Ohio. The formation is also recognized in Alabama. It is a major ridge-former In the Ridge-and-Valley Appalachians of the eastern United States...		φp
Mississippian		Mauch Chunk Formation Mauch Chunk Formation The Mississippian Mauch Chunk Formation is a mapped bedrock unit in Pennsylvania, Maryland, and West Virginia. It is named for the borough of Mauch Chunk, now known as Jim Thorpe, Pennsylvania.-Description:...		Mmc
Mississippian		Pocono Formation Pocono Formation The Mississippian Pocono Formation is a mapped bedrock unit in Pennsylvania, Maryland, and West Virginia, USA. It is also known as the Pocono Group in Maryland and West Virginia,... (Burgoon Formation)		Mp (Mb)
Mississippian/Devonian		Spechty Kopf Formation
Mississippian/Devonian		Rockwell Formation Rockwell Formation The Rockwell Formation is a late Devonian and early Mississippian mapped bedrock unit in West Virginia, Maryland, and Pennsylvania, in the United States.-Description:...
Mississippian/Devonian		Huntley Mountain Formation Huntley Mountain Formation The Huntley Mountain Formation is a late Devonian and early Mississippian mapped bedrock unit in Pennsylvania, in the United States.-Description:The formation is composed of relatively soft grayish-red shale and olive-gray sandstone...
Devonian Devonian The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...		Catskill Formation		Dck
Devonian		Brallier Formation Brallier Formation The Devonian Brallier Formation is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.-Description:The Brallier Formation was described by Charles Butts in 1918 as a fine-grained, siliceous shale with few fine-grained sandstone layers, from outcrops in central Pennsylvania...		Db
Devonian		Harrell Formation Harrell Formation The Devonian Harrell Formation is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.-Description:The Harrell Formation was first described by Charles Butts in 1918...		Dh
Devonian	Hamilton Group Hamilton Group The Devonian Hamilton Group is a mapped bedrock unit in New York, Pennsylvania, Maryland, and West Virginia. In Virginia, it is known as the laterally equivalent Millboro Shale.The group is named for the village of Hamilton, New York...	Mahantango Formation Mahantango Formation The Devonian Mahantango Formation is a mapped bedrock "unit" in Pennsylvania, New Jersey, New York and Maryland. It is named for the North branch of the Mahantango Creek in Perry and Juniata counties in Pennsylvania. It is a member of the Hamilton Group, along with the underlying the Marcellus...		Dmh
Devonian	Hamilton Group	Marcellus Formation Marcellus Formation The Marcellus Formation is a unit of marine sedimentary rock found in eastern North America...		Dm
Devonian		Onondaga Formation		Do
Devonian		Old Port Formation Old Port Formation The Devonian Old Port Formation is a mapped bedrock unit in Pennsylvania, Maryland, and West Virginia. Members of the unit are also mapped in New Jersey and Virginia as parts of other formations or groups.-Description:...		Dop
Devonian		Old Port Formation	Ridgeley Member Ridgeley sandstone The Ridgeley sandstone is a sandstone or quartzite of Devonian age found in the Appalachian Mountains of Pennsylvania, Maryland, West Virginia, and Virginia, USA. The Ridgeley is fine-grained, siliceous, calcareous in its lower strata, sometimes fossiliferous, and sometimes locally pebbly or...	Dr
Devonian/Silurian		Keyser Formation Keyser Formation The Late Silurian to Early Devonian Keyser Formation is a mapped limestone bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia.-Description:...		DSk
Silurian Silurian The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...		Tonoloway Formation Tonoloway Formation The Late Silurian Tonoloway Formation is a mapped limestone bedrock unit in Pennsylvania, Maryland, Virginia and West Virginia.-Description:The basal 50 m consists of medium-dark-gray laminated to thin-bedded calcisiltite with shale partings and interbeds. Overlying 5 m are light-yellowish-gray to...		Sto
Silurian		Wills Creek Formation Wills Creek Formation The Silurian Wills Creek Formation is a mapped bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia.-Description:The Wills Creek is defined as a moderately well bedded greenish-gray shale containing local limestone and sandstone zones, or more specifically as an olive to...		Swc
Silurian		Bloomsburg Formation Bloomsburg Formation The Silurian Bloomsburg Formation is a mapped bedrock unit in Pennsylvania, New Jersey, New York and Maryland. It is named for the Town of Bloomsburg, Pennsylvania for which it was first described. The Bloomsburg marked the first occurrence of red sedimentary rocks in the Appalachian Basin...		Sb
Silurian		Mifflintown Formation		Sm
Silurian	Clinton Group Clinton Group The Silurian Clinton Group is a mapped bedrock unit in New York, Pennsylvania, Maryland, and West Virginia. It contains the Rochester Shale, Rose Hill Formation and the ridge-forming Keefer Formation...	Keefer Formation		Sk
Silurian	Clinton Group	Rose Hill Formation		Srh
Silurian		Tuscarora Formation Tuscarora Formation The Silurian Tuscarora Formation — also known as Tuscarora Sandstone or Tuscarora Quartzite — is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.-Description:...		St
Silurian		Shawangunk Formation Shawangunk Formation The Silurian Shawangunk Formation is a mapped bedrock unit in eastern Pennsylvania, New Jersey, and New York. It is named for the Shawangunk Ridge for which it is the dominant rock type. The division of the Shawangunk between the Tuscarora Formation and Clinton Group has not been conclusively...		Ss
Ordovician Ordovician The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...		Juniata Formation Juniata Formation The Ordovician Juniata Formation is a mapped bedrock unit in Pennsylvania and Maryland. It is a relative slope-former occurring between the two prominent ridge-forming sandstone units: the Tuscarora Formation and the Bald Eagle Formation in the Appalachian Mountains.-Description:The Juniata is...		Oj
Ordovician		Bald Eagle Formation Bald Eagle Formation The Ordovician Bald Eagle Formation is a mapped bedrock unit in central Pennsylvania, USA. It is a ridge-forming unit in the Appalachian Mountains.-Description:...		Obe
Ordovician		Reedsville Formation Reedsville Formation The Ordovician Reedsville Formation is a mapped surficial bedrock unit in Pennsylvania, Maryland, Virginia, West Virginia, and Tennessee, that extends into the subsurface of Ohio. This rock is a slope-former adjacent to the prominent ridge-forming Bald Eagle sandstone unit in the Appalachian...		Or
Ordovician		Martinsburg Formation Martinsburg Formation The Ordovician Martinsburg Formation is a mapped bedrock unit in Pennsylvania, New Jersey, Maryland, Virginia, and West Virginia. It is named for the town of Martinsburg, West Virginia for which it was first described...		Om
Ordovician	Trenton Group	Coburn Formation
Ordovician	Trenton Group	Salona Formation
Ordovician	Trenton Group	Nealmont Formation
Ordovician		Benner Formation		Om
Ordovician		Bellefonte Formation Bellefonte Formation __notoc__The Ordovician Bellefonte Formation is a mapped bedrock unit in central Pennsylvania.-Description:The Bellefonte is defined as a medium-gray, brownish-weathering, medium-bedded dolomite and minor sandstone...		Obf
Ordovician		Axeman Formation		Oa
Ordovician		Nittany Formation		On
Ordovician		Stonehenge/Larke Formation		Osl
Cambrian Cambrian The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...		Warrior Formation Warrior Formation The Cambrian Warrior Formation is a mapped limestone bedrock unit in Pennsylvania.-Description:The Warrior Formation is described by Berg and others as gray, thin- to medium-bedded, fossiliferous, cyclic limestone bearing stromatolites, interbedded with shale, siltstone, and sandstone.-Fossils:*...		Cw
Cambrian		Chickies Formation Chickies Formation The Cambrian Chickies Formation is a mapped bedrock unit in Pennsylvania and Maryland. It is named for Chickies Rock, north of Columbia, Pennsylvania along the Susquehanna River.-Description:...		Cch
Cambrian/Ediacaran Ediacaran The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...		Wissahickon Formation Wissahickon Formation The Wissahickon Formation is a mapped bedrock unit in Pennsylvania, New Jersey, and Delaware. In Maryland, the term "Wissahickon" is no longer used and has since been divided into several units. It is named for the Wissahickon gorge in Fairmount Park, Philadelphia.-Description:The Wissahickon is...		CZw
Mesoproterozoic Era		Baltimore Gneiss		Ybg

Note: Some of the Formations are laterally equivillant in age. They are listed in order from West to East in this case.

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