The focal point of the geologic story of McCormick's
Creek State Park is the canyon. A mile long, more than
100 feet deep, and with limestone outcrops along the walls,
the canyon brings to mind many questions. This brief summary
is intended to answer most of the geologic questions that visitors
ask, but the entire story is a long one and many of the details
are still unknown.
Some 250 million years ago Indiana was covered by a broad,
shallow sea. Limy mud and sand were deposited layer by layer
on the sea bottom. As these soft sediments became deeply buried,
they were compressed and cemented into layers of solid limestone.
Geologists have divided these rocks into three formations, which
lay on top of one another like a stack of pancakes. All three
bedrock formations date from the Mississippian Period of geologic
time, and together they represent about a million years of geologic
Bedrock Of The Canyon Walls
The lowest, and therefore the oldest, of these formations is
the Salem Limestone, which can be seen in the old quarry near
the mouth of the canyon and in the lower canyon walls. The limestone
is in the thick beds, is uniformly sandy in texture, and weathers
into huge rounded blocks. Some surfaces show a pitted effect
known as honeycomb weathering. Only a few large fossils are
present, but with a magnifying glass you may be able to see
that most of the sand grains are small fossils or rounded fossil
fragments. Many are the shells of Endothyra baileyi,
a single-celled animal that lived in abundance in the ancient
sea and was no bigger than a pinhead.
The middle formation is the St. Louis Limestone. This layer
is about 60 feet thick and makes up most of the canyon walls.
It is more fine-grained and more closely cemented than the Salem
Limestone. Some of the beds are shaly and some contain nodules
of chert, a hard flinty material. Among the fossils that are
abundant in some beds are colonial corals, such as Lithostrotionella.
Observe but please don't collect specimens in the park.
The St. Louis Limestone ends at a height about equal to the
top of the falls. Upper parts of the canyon walls are made up
of the third formation, the Ste. Genevieve Limestone. Rocks
of this formation are even more fine grained, more smooth textured,
and more compact than those below. The Ste. Genevieve Limestone
is the youngest bedrock of the park.
How The Canyon Was Formed
Long after the rocks were formed, they were lifted above sea
level, and streams began their work of erosion. Valleys similar
to those of today were formed. Then, about a million years ago,
a series of glaciations began that powerfully shaped the topography
of this part of Indiana.
The glacier that covered the park area is known as the Illinoian
glacier. It left deposits of sand and clay that contain cobbles
of granite and other stones from as far north as Ontario. These
deposits show that the limit of this glacier's advance was just
southeast of the park. The ice blocked many of the pre-glacial
valleys, and drainage from these valleys, along with meltwater
from the glacier, had to flow southwestward along the glacier
margin for many miles before it could find an outlet to the
When the ice melted, glacial deposits still blocked some of
the pre-glacial valleys. Some of the streams that drained these
valleys did not find their former courses but eroded new ones.
The area southeast of the park formerly drained westward, but
glacial deposits diverted the drainage to the northwest across
what is now the park, and in this way the course of McCormick's
Creek was determined.
As the creek eroded downward, the rock-walled canyon was formed.
Most of this erosion probably took place about 50,000 years
ago, when ice of the last glaciation (which did not reach the
park area) was advancing from the north. At that time the climate
was wetter and colder, and erosion was more rapid than it is
today. The falls, which are evidence of the canyon-forming process,
still are eroding their way upstream, but now at a very slow
Sinkholes, Caves and Natural Bridges
In the upland area of the park are numerous bowl-shaped depressions
called sinkholes. Some are small, some are large, and some are
in groups or in rows. A few contain springs and small streams
that sink into the ground. All these features were formed by
the underground movement of water, which slowly dissolves the
limestone bedrock and forms an underground network of passageways
to carry the water. Sinkholes, which are formed as the limestone
is slowly removed from beneath the soil, carry the runoff from
rain and snow underground.
As the underground streams seek lower and lower levels, some
of the passageways are left high and dry. Wolf Cave is an example
of a large dry passageway that has been opened to view by erosion.
Erosion also leaves small remnants of the passage as natural
bridges. Litten Natural Bridges are an example. Features formed
by subterranean drainage are known as karst features and are
widespread in part of southern Indiana where limestone is found.
Information provided by Indiana Department
of Natural Resources brochure on the Geology of McCormick's
Creek State Park. Thanks to Henry H. Gray and the Indiana Geologic
Survey for development of this information in 1977.
Want to know even more about the geology, history, plants or
animals of McCormick's Creek State Park?
Check out the Nature Center
for exhibits, brochures, interpretive services and more.