A

A'

WILLIAMS FULTON LUCAS

OTTAWA

WOOD

HENRY

DEFIANCE

HARDIN

HANCOCK

AUGLAIZE

ALLEN

PUTNAM

MERCER

VAN WERT

PAULDING

HOLMES

ERIE SANDUSKY

SENECA HURON

LORAIN

MEDINA

CRAWFORD RICHLAND ASHLAND WAYNE

MORROW

WYANDOT

MARION

CARROLL

STARK COLUMBIANA

MAHONING

TRUMBULL

PORTAGE

SUMMIT

GEAUGA

ASHTABULA

LAKE

CUYAHOGA

UNION

DELAWARE

KNOX

COSHOCTON

TUSCARAWAS

HARRISON

JEFFERSON

FAYETTE

PICKAWAY

FRANKLIN MADISON

CLARK

MONTGOMERY PREBLE

CHAMPAIGN

MIAMI

LOGAN

SHELBY

DARKE

BROWN

HIGHLAND

GREENE

CLINTON WARREN

CLERMONT

HAMILTON

BUTLER

BELMONT

GUERNSEY

NOBLE MONROE

MUSKINGUM

MORGAN

WASHINGTON

LICKING

PERRY FAIRFIELD

HOCKING

ATHENS

MEIGS

VINTON

JACKSON

GALLIA

LAWRENCE

ROSS

PIKE

ADAMS

SCIOTO

Glacial

Margin

A A'

BEDROCK GEOLOGIC MAP OF OHIO

0

0

10 20 30 40 miles

10 20 30 40 50 kilometers

Quaternary

(cross section only)

Permian-Pennsylvanian

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Ordovician-Cambrian

(cross section only)

Neoproterozoic

(cross section only)

Mesoproterozoic

(cross section only)

Fault

Key

Serpent Mound

Impact Structure

Serpent Mound

Impact Structure

APPALACHIAN BASIN

BELLEFONTAINE

MICHIGAN BASIN OUTLIER Glacial Margin

GRANITE-RHYOLITE PROVINCE EAST CONTINENT RIFT BASIN GRENVILLE PROVINCE Bend in section

HIGHLAND

PIKE

ADAMS

1 mi

Recommended citation: Ohio Division of Geological Survey, 2006, Bedrock geologic map of Ohio: Ohio Department of Natural Resources, Division of Geological Survey Map BG-1, generalized page-size version with text, 2 p., scale 1:2,000,000.

STATE OF OHIO • DEPARTMENT OF NATURAL RESOURCES • DIVISION OF GEOLOGICAL SURVEY
This map is a generalization of the Bedrock Geologic Map of 

Ohio (Slucher and others, 2006)—the fi rst statewide 1:500,000-scale 

bedrock-geology map compiled by the Ohio Division of Geological 

Survey since 1920 and the fi rst to properly portray the bedrock 

geology that exists beneath the extensive deposits of Quaternary 

sediments that cover much of the bedrock in the state. Overall, 

the bedrock geology of Ohio consists of fl at lying to gently dipping 

carbonate, siliciclastic, evaporite, and organoclastic strata of sedimentary origin that range in age from Upper Ordovician to Upper 

Carboniferous-Lower Permian. At depth, as illustrated in the cross 

section, older sedimentary, igneous, and metamorphic rocks that 

range from Lower Ordovician to Mesoproterozoic in age occur. At 

the surface, an irregular veneer of mainly unconsolidated Quaternary sediments conceal most bedrock units occurring northward 

and westward of the glacial margin.

Strata of the Ordovician System are the oldest exposed rocks 

in Ohio and consist mainly of alternating shale and limestone sequences. Silurian System strata are mostly dolomites with lesser 

amounts of shale. Rocks of the Devonian System consist of two contrasting types. Lower and Middle Devonian-age strata are mainly 

carbonate rocks whereas Upper Devonian-age rocks consist mostly 

of clastic rocks. In Champaign and Logan Counties, Devonian rocks 

occur on a small erosional remnant referred to as the Bellefontaine 

Outlier by geologists. Coincidentally, the highest topographic point 

in Ohio (Campbell Hill–1,549 feet above sea level) occurs also in 

this area.

The Carboniferous System is divided into two Subsystems, the 

Mississippian and Pennsylvanian. Mississippian strata are mostly 

shales and sandstones that occur locally in various proportions. 

Pennsylvanian strata consist mainly of a diverse array of alternating sandstones, siltstones, shales, mudstones, limestones, and underclays; economic coal beds occur also in portions of this sequence. 

The youngest interval of sedimentary rocks in Ohio, the Dunkard 

Group, occurs only in southeastern Ohio and consists of strata 

similar in composition to the underlying Upper Pennsylvanianage rocks; however, the age of the Dunkard Group has been debated since the late 1800s. Dunkard strata contain a well-studied 

late Pennsylvanian-age assemblage of plant fossils with infrequent 

early Permian-age forms. Yet, fossil plant spores found in coal beds 

in the interval only support a late, but not latest Pennsylvanian 

age. Thus, until more defi nitive fossils are found, geologist are unable to determine the exact age of the Dunkard Group beyond a 

combined Permian-Pennsylvanian age assignment.

In west-central Ohio, the ancient Teays River system extended 

across much of Ohio during the late Neogene to early Quaternary 

Periods and sculptured an extensive network of deeply dissected 

valleys into the bedrock surface. The spatial confi guration of many 

geologic units on this map clearly refl ects the major channel networks of these former drainage systems. Also, four major regional 

structural geology elements affect the spatial distribution of rocks 

in Ohio: the Appalachian and Michigan basins, and the Cincinnati 

and Findlay arches which occur between the two basins. Locally, 

several high-angle normal faults displace rocks in the state.

The Serpent Mound Impact Structure in southern Ohio is a 

circular area of deformed and broken rocks that is approximately 

four and one-half miles in diameter. Recent investigations indicate 

the feature is the result of a meteorite impact believed to have occurred between 256 and 330 million years ago.

Cross section A-A' traverses Ohio from the northwest to the 

southeast and intersects the southern portion of the Michigan Basin, the area between the Cincinnati and Findlay arches, and the 

western Appalachian Basin, respectively. The stratigraphic units 

shown in this profi le illustrate the broad, arching geometric distortion to the bedrock in Ohio created mainly by periods of tectonic 

subsidence within these regional structural basins. For specifi c 

details on the various rock units, economic commodities, and geologic hazards within Ohio, see either the printed or digital version 

of the Bedrock Geologic Map of Ohio (Slucher and others, 2006). 

Both products are available for purchase by contacting the ODNR 

Geologic Records Center by calling 614-265-6576 or emailing:

geo.survey@dnr.state.oh.us.

Quaternary (about 1.8 million years ago to present)—Unconsolidated sediments: till, gravel, sand, silt, clay, and organic 

debris. Continental origin. (Shown in cross section only)

Period of widespread erosion

Permian and Pennsylvanian (about 298 to 302 million years 

ago)—Sedimentary rocks: mainly shale, sandstone, siltstone, 

mudstone, and minor coal. Continental origin.

Pennsylvanian (about 302 to 307 million years ago) Sedimentary rocks: mainly shale, sandstone, siltstone, mudstone, limestone, and some coal. Continental and marine origin.

Pennsylvanian (about 307 to 318 million years ago)—Sedimentary rocks: mainly sandstone, siltstone, shale, and conglomerate, with some coal and limestone. Deltaic and marine origin.

Period of widespread erosion

Mississippian (about 322 to 359 million years ago)—Sedimentary rocks: sandstone, shale, siltstone, conglomerate, and minor limestone. Marine to marginal marine origin.

Devonian (about 359 to 385 million years ago)—Sedimentary 

rocks: mainly shale and siltstone with some sandstone. Marine to marginal marine origin.

Devonian (about 385 to 407 million years ago)—Sedimentary 

rocks: mainly limestone and dolomite with some shale, and 

minor sandstone. Marine and eolian origin.

Period of widespread erosion

Silurian (about 416 to 423 million years ago)—Sedimentary 

rocks: dolomite, anhydrite, gypsum, salt, and shale. Marine 

and restricted marine origin.

Silurian (about 423 to 435 million years ago)—Sedimentary 

rocks: dolomite and shale with some limestone. Marine origin.

Period of widespread erosion

Ordovician (about 446 to 450 million years ago)—Sedimentary 

rocks: shale and limestone. Marine origin.

Ordovician (about 450 to 460 million years ago)—Sedimentary 

rocks: limestone and shale. Marine origin.

Period of widespread erosion

Ordovician and Cambrian (about 486 to 510 million years ago)—

Sedimentary rocks: mainly dolomite, sandstone, shale, with minor limestone. Marine origin. (Shown in cross section only)

Period of widespread erosion

Neoproterozoic (between 900 million and 1 billion years 

ago)—Metamorphic rocks: gneiss, schist, amphibolite, and 

marble; and igneous rocks: granite. Form during collision of 

tectonic plates. (Shown in cross section only)

Mesoproterozoic (between 1.0 and 1.2 billion years ago)—Sedimentary rocks: sandstone and siltstone; and igneous rocks: basalt and rhyolite. Form during rifting of continental landmass. 

(Shown in cross section only)

Period of widespread erosion

Mesoproterozoic (between 1.45 and 1.52 billion years ago)—Igneous rocks: granite and rhyolite. Formed during crustal evolution and differentiation. (Shown in cross section only)