This document summarizes the geologic history of West Branch State Park in Ohio. The bedrock underneath the park consists of Devonian to Pennsylvanian shale and sandstone formations that were deposited in marine environments. During the last ice age, the Wisconsinan glacier advanced over the area, eroding the bedrock and depositing glacial sediments. These sediments included tills that formed ground and end moraines across the park. The glacier also filled an ancient buried stream valley with 350 feet of drift, which is now occupied by the Mahoning River and reservoir. Today, the park sits atop these glacial sediments, providing insight into the area's bedrock and glacial geological past.

1. Discovering the Bedrock and Glacial Geologic History ofDiscovering the Bedrock and Glacial Geologic History of
West Branch State Park, OhioWest Branch State Park, Ohio
TIMKO, Samuel B. C., stimko3@kent.edu, SCHUSTER, Kelsey M., kshust2@kent.edu, and HACKER, David B., Kent, OH 44242
Department of Geology
Kent State University, Kent, OH 44242
Abstract
West Branch State Park is located on the west branch
of the Mahoning River in Portage County. In 1965, the
Michael J. Kirwan Reservoir was completed on the river for
flood control, water supply, recreation, and fish and wildlife
management. However, detailed geologic information of
the park is lacking for the public to understand its ancient
history. A detailed investigation was conducted to better
constrain the geologic history of West Branch State Park.
Detailed information of the park was gathered
through extensive fieldwork and published data. Bedrock
and glacial geologic maps were constructed using ArcGIS
and MicroDEM mapping programs. Thickness of glacial
material and bedrock formations were determined using
ground water well data. A north-south cross section
through the park was produced, showing the geology in the
third dimension.
West Branch State Park is situated on the glaciated
plateau of northeastern Ohio where Pleistocene glaciers
were able to override the gentle hills and stream valleys of
the land formerly uplifted as part of the Appalachian
Mountain building process. The subsurface bedrock units in
the park consist of Devonian to Pennsylvanian shales and
sandstones. The bedrock was covered by several ice
advances of the Wisconsinan Glacier that left behind three
distinct glacial features: a buried stream valley filled with
~350 feet of drift material, now occupied by the present
stream and reservoir; ground moraine, ~15 feet thick,
covering the hills on the southern section of the park; and
the Kent End Moraine on the northern part of the park.
Glacial Till
Wisconsinan
GlaciationBedrock
Geology
History and
Features
Glacial till is the general term for unsorted sediment
that is directly deposited by the advancing or melting of a
glacier. It is made up of sediments previously eroded by the
glacier. West Branch features both ground moraines and end
moraines, which are two different types of till and
depositional areas, and outwash areas.
Ground moraines are areas of hilly topography, notable
for a lack of sharp ridges, and form at the base of glaciers.
End moraines typically feature ridges and layers of sediment
that were deposited at the edge of glacial advancement, and
are used to mark the boundaries of glacial ice. Outwash is
sediment, usually sand or silt, carried by running water from
the melting of a glacier and deposited in plain areas.
South of the park is the Hiram ground moraine, which
consists of clay sized particles. The Lavery ground moraine
is located south, east, and northeast of the park, and is made
up of silt sized sediments. The Kent end moraine is located
to the north, and is made up of silty sediments. The Outwash
plain lies to the north of the Kent end moraine, and is
comprised of sandy and silty sediments.
The bedrock layers of West Branch State Park consist
primarily of shales and sandstones. Shale is a fine-grained
sedimentary rock composed of mud, clay minerals, and silt sized
particles. Sandstone is a coarse-grained sedimentary rock
composed of fine to coarse sand sized particles, and minerals
such as quartz and feldspar. Both are typically deposited in
shallow marine environments or transitional environments
(beaches, deltas, etc.).
The named layers include, from youngest to oldest:
Homewood Sandstone Member, Mercer Shale Member,
Connoquenessing Sandstone Member, Sharon Shale Member,
Sharon Sandstone-Conglomerate Member, Cuyahoga
Sandstone-Shale, Berea Sandstone, and Pre-Berea Rocks, which
consists of undifferentiated layers of shale and sandstone.
The Wisconsinan Glacier was that last great glacier present in
Ohio during the Pleistocene Epoch, commonly known as the Ice Age.
As global temperatures cooled, the glacier began to form in Canada
70,000 years ago, and began its slow advance to Ohio, reaching the state
about 24,000 years ago. Eventually, the glacier had retreated from the
state 14,000 years ago, but not before eroding some of the bedrock and
depositing a large volume of glacial sediment. The Wisconsinan had a
major impact on the northeast area of the state, including shaping the
topography present in West Branch and the surrounding areas to what
we see today.
Acknowledgements
Ohio Geological Survey
Ohio Department of Natural Resources
United States Geologic Survey
Kent State University Map Library
Special Thanks to Stacee Stinedurf for all her
dedication and hard work
The geologic features of West Branch State Park, while
not as fantastic as Zion National Park or the Grand Canyon,
are still unique in its own way. Bedrock, unexposed in the park
proper, but visible in some areas surrounding the reservoir,
was deposited during the Devonian (416-359 mya),
Mississippian (359-318 mya) , and Pennsylvanian (318-299
mya) ages during the Paleozoic Era. Erosion, mainly by stream
action, removed any younger rocks that may have been
deposited after this time period. The arrival of the
Wisconsinan glacier during the Ice Age then filled in these
valleys with glacial sediments. Atop one of these buried
valleys sits West Branch State Park and the Michael J. Kirwan
Reservoir.
An outcrop of sandstone located along Rock
Spring Road, south of the park entrance.
Clayey glacial till exposed along the lake
shore near the park campground.
Wentworth Grain Size Chart derived from published data on pubs.usgs.gov