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.
"AWESOME! Our tour guide was great. I know I'll be back again. Thanks!"
- Comment from a visitor
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".
Fun Fact
The Cave has the same temperature everyday, all year long! 50 degrees F.
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.
Fun Fact
Over 59,000 people came to visit the Cave in the first 8 weeks of operation.
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.
Come help us celebrate 70 years during our annual Discovery Days!
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!
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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