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Cave of the Mounds - National Natural Landmark provides an excellent introduction to caving in the midwest. This page is a great place to start to learn more about
the science and history of our Cave, as well as discover neat general caving facts like nicknames given for various formations, meanings of spelunking, and safety tips! Follow the
links below or just scroll down to learn more.
Overview of the Cave
 The
most beautiful cave in Wisconsin and the upper Midwest, Cave of the Mounds lies just off U.S. Highways
18/151 in Blue Mounds, WI. The United States Department
of the Interior and the National Park Service designated
Cave of the Mounds a National Natural Landmark because the
site possesses "exceptional value as an illustration
of the nation’s natural heritage and contributes to
a better understanding of man’s environment". Curious tourists and budding cave enthusiasts have been enjoying an introduction to caving in the midwest for years while visiting Cave of the Mounds.
Commonly referred to as the "jewel
box" of America’s major caves for the variety and delicacy
of its formations, Cave of the Mounds is recognized by the
Chicago Academy of Sciences as "the significant cave
of the upper Midwest".
A guided tour of the Cave takes you past
a varied collection of colorful stalactites, stalagmites,
columns and other formations. The main cavern began forming
over a million years ago as acidic water dissolved the limestone
bedrock far below the surface. As Cave of the Mounds staff
like to point out, geologic time is mind-boggling. It is
difficult to imagine the time it took for the large caverns
to be dissolved within rock that is itself believed to be
over 400 million years old!
A lower meandering portion of the Cave
was formed by the rushing water of an underground stream.
The contrast between the chemical and mechanical processes of
cave formation is one of the geologic lessons illustrated
on The Cave Tour.
People who come to the Cave of the Mounds
in the summer appreciate the constant 50-degree temperature.
They also enjoy the park-like grounds, with picnic areas, walking trails and
rock gardens. Winter visitors can take advantage of the
Cave’s comparative warmth. The Cave is open
in the winter on weekends, and during the week by advance
reservation.
Guided tours of Cave of the Mounds are
available year 'round. Special rates are
available to groups of 20 or more by advance reservation
only. Cave of the Mounds is located just 20 miles west of Madison,
off U.S. Highways 18/151.
History of the Cave
Fun Fact
Over 59,000 people came to visit the
Cave in the first 8 weeks of operation.
Learn
more fun facts. |
Cave of the Mounds takes its name from
the Blue Mounds, two large hills which have long been Wisconsin
landmark features. The West Mound, at 1716 feet, is the highest
point in Southern Wisconsin; the East Mound reaches 1489
feet. Cave of the Mounds lies under the southern slope of
the East Mound.
This area was settled by Ebenezer Brigham,
a successful lead miner who became Dane County’s first
permanent white settler in 1828. The West Mound is now a
Wisconsin state park; part of the East Mound still belongs
to the Brigham family. Brigham County Park lies along the
wooded northern edge of this East Mound. Both parks afford
magnificent vistas of southern Wisconsin.
 Ebenezer
Brigham traveled from Massachusetts down the Ohio River
and up the Mississippi to join the Wisconsin lead rush in
the late 1820’s. He established his "diggings"
and built a smelting furnace and a house just north of the
Cave. His house became a trading post, an inn, a stagecoach
stop, and Dane County’s first post office. Colonel
Brigham helped build and later commanded Fort Blue Mounds
during the Blackhawk War in 1832. Ebenezer lived a long
life on his Bringham Farm never realizing that a greater
discovery than lead lay deep beneath its surface.
Cave of the Mounds was accidentally discovered
on August 4, 1939. Workers, who were
removing high quality limestone from a quarry on the Brigham Farm, blasted into the Cave.
The blast tore the face off the quarry and revealed a great
underground cavern. All quarrying stopped and never
resumed. The dynamite blast revealed a limestone cave
more than twenty feet high opening into other rooms and
galleries, all containing numerous mineral formations.
 The
excitement of the discovery brought so many curiosity seekers
that the Cave had to be closed in order to preserve it.
Soon, lights and wooden walkways were installed. And, in
May 1940, Cave of the Mounds was opened to visitors. Millions
of visitors later, the Cave’s wooden walkways were replaced with concrete; a large stone building
replaced the original entry building; and theatrical lighting
has been installed to dramatize the colors and shapes within
the Cave. Picnic areas, walking trails, rock gardens, gift shops and a visitor
center have all since been developed.
Science of the Cave
The story of the geologic formation of
the Cave of the Mounds begins with the creation of the rock
in which the Cave formed. The Cave was formed within limestone, a sedimentary
rock formed from compacted seashells and other marine sediments. This rock
dates back  over
400 million years to the Ordovician Period of the Earth’s
geologic history. During the Ordovician Period, warm shallow
seas covered the continent where we find Wisconsin today.
Abundant shell life could thrive in these seas. Layers and
layers of calcium carbonate shell debris accumulated and
slowly hardened into the limestone we see today. Thousands of feet of limestone
and other sedimentary rocks were laid down during this Ordovician
Period. Millions of years ago, the seas receded leaving
these layers of rock behind and erosion began to wear them
down. Today the exposed rock in Blue Mounds is a limestone
called Galena dolomite, which is a specific kind of limestone
containing aat least 20% magnesium.
Cave of the Mounds itself began to form
1 or 2 million years ago when the Galena dolomite
was still beneath the water table. The water table is defined
as that level below which all of the rock is saturated with
water. Often, the top layer of the water table becomes acidic
because rainwater and melting snow absorb carbon dioxide
as they seep through surface soils. The water combines with
the carbon dioxide to form weak carbonic acid, which can
dissolve limestone and create cavities within the rock.
When a major crack lets large amounts of acidic water into
the limestone below the water table, large amounts of rock
dissolve along this crack. This is what happened at Cave
of the Mounds. The Cave was formed along a major crack that
can still be seen today. This crack is called the "lifeline"
of the Cave.
The story of Cave of the Mounds does not
end with the dissolution of limestone to form the hollow
cavern. Even as the dolomite beneath the ground was being
dissolved to form the Cave, surface streams were eroding
deeper and deeper valleys in the landscape. As the stream
levels lowered, so did the water table. Eventually, the
water table dropped below the level where the cave had been
formed. Now, the large natural cavity far below the earth’s
surface was filled with air. This allowed a new stage in
the life of the Cave to begin.
When surface water seeps through the soil
and then through the porous rock, it dissolves
small amounts of the limestone (also called calcium carbonate). Every droplet of water entering
the cave below carries dissolved calcium carbonate. As the
water drops enter the air-filled cave, this calcium carbonate
is precipitated in the form of calcite. Each drop leaves
calcite crystals on the cave ceiling, walls or floor. The
crystals adhere to each other and grow into different kinds
of formations, called speleothems. Eventually, stalactites reach down from the
ceiling, stalagmites tower upward from the floor, and sheets
of flowstone cover the walls.
Speleothems grow very slowly. The rate of growth
depends on how fast the water flows and on how much dissolved
calcium carbonate it contains. It can take from 50 to 150
years to deposit one cubic inch of "cave onyx".
This process continues today – a design forever in
process and never complete.
Learn more about the science of the Cave
on our Cave geology page!
Designation of the Cave
In 1988, Cave of the Mounds was designated a National Natural
Landmark by the United States Department of the Interior
and the National Park Service. In receiving this honor,
Cave of the Mounds was recognized as "a site which
possesses exceptional value as an illustration of the nation’s
natural heritage and contributes to a better understanding
of man’s environment."
The National Natural Landmark designation is made by the Secretary of the Interior after in-depth
scientific study of a potential site. The selection process
is rigorous: to be considered for National Natural Landmark
status, a site must be one of the best examples of a natural
region’s characteristic biotic or geologic features.
Cave of the Mounds is a natural limestone cave and is exemplary
of this type of solution cave which forms as part of a karst landscape,
such as is found in southwestern Wisconsin. What makes Cave
of the Mounds special is the quantity and quality of its many speleothems, and the extraordinary colors left behind by minerals naturally present in the rock. Cave of the Mounds is often referred
to as the "jewel box" of America’s major
caves because of the variety, color and delicacy of its formations.
Our National Natural Landmark plaque is
prominently displayed on the Cave Entrance Building. Cave
of the Mounds is proud to be a participant in the National
Natural Landmark Program. We are committed to the preservation
of this unique geologic formation and the land which surrounds
it, and we encourage visitors to come experience some of the most beautiful show caving in the midwest!
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