List of mapped rock formations in Pennsylvania

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The following is a list of the mapped bedrock units in Pennsylvania. The rocks are listed in stratigraphic order.[1]

System Group name Formation name Member name Map symbol[2]
Triassic Newark Group Passaic Formation Trp
Triassic Newark Group Lockatong Formation Trl
Triassic Newark Group Stockton Formation Trs
Permian Dunkard Group Greene Formation Pg
Permian Dunkard Group Washington Formation Pw
Pennsylvanian Conemaugh Group Cassleman Formation φcc
Pennsylvanian Conemaugh Group Glenshaw Formation φcg
Pennsylvanian Allegheny Formation φa
Pennsylvanian Llewellyn Formation φl
Pennsylvanian Pottsville Formation φp
Mississippian Mauch Chunk Formation Mmc
Mississippian Pocono Formation
(Burgoon Formation)
Mississippian/Devonian Spechty Kopf Formation
Mississippian/Devonian Rockwell Formation
Mississippian/Devonian Huntley Mountain Formation
Devonian Catskill Formation Dck
Devonian Brallier Formation Db
Devonian Harrell Formation Dh
Devonian Hamilton Group Mahantango Formation Dmh
Devonian Hamilton Group Marcellus Formation Dm
Devonian Onondaga Formation Do
Devonian Old Port Formation Dop
Devonian Old Port Formation Ridgeley Member Dr
Devonian/Silurian Keyser Formation DSk
Silurian Tonoloway Formation Sto
Silurian Wills Creek Formation Swc
Silurian Bloomsburg Formation Sb
Silurian Mifflintown Formation Sm
Silurian Clinton Group Keefer Formation Sk
Silurian Clinton Group Rose Hill Formation Srh
Silurian Tuscarora Formation St
Silurian Shawangunk Formation Ss
Ordovician Juniata Formation Oj
Ordovician Bald Eagle Formation Obe
Ordovician Reedsville Formation Or
Ordovician Martinsburg Formation Om
Ordovician Trenton Group Coburn Formation
Ordovician Trenton Group Salona Formation
Ordovician Trenton Group Nealmont Formation
Ordovician Benner Formation Om
Ordovician Bellefonte Formation Obf
Ordovician Axeman Formation Oa
Ordovician Nittany Formation On
Ordovician Stonehenge/Larke Formation Osl
Cambrian Warrior Formation Cw
Cambrian Chickies Formation Cch
Cambrian/Ediacaran[3] Wissahickon Formation CZw
Mesoproterozoic Era Baltimore Gneiss Ybg

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


  1. ^ Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.
  2. ^ Berg, T.M., Edmunds, W.E., Geyer, A.R. and others, compilers, (1980). Geologic Map of Pennsylvania: Pennsylvania Geologic Survey, Map 1, scale 1:250,000.
  3. ^ Blackmer, G.C., (2005). Preliminary Bedrock Geologic Map of a Portion of the Wilmington 30- by 60-Minute Quadrangle, Southeastern Pennsylvania. Pennsylvania Geologic Survey, Open-File Report OFBM-05-01.0.

See also[edit]