 |
| A column at Wisconsin's Cave of the Mounds. |
 |
| A one-hour tour takes visitors into the cave. |
The one-hour walking tour covers about 0.66 miles. Cave of the Mounds is among Wisconsin’s best known caves with more than 100,000 annual visitors.
To reach the cave, from Mt. Horeb take Bus. U.S. 18 west of town. Turn right/west onto County Hwy. ID. Once near Blue Mounds, go right/northwest onto Cave of the Mounds Road. The parking lot is on the road’s left/southwest side. From the lot, walk to the visitor center for tour tickets.
Quarry workers discovered the cave in 1939 when their blasting operations revealed an underground cavern more than 20 feet high and linked to other rooms. Visitors flocked to see the caves, so lights and walkways were installed the following year.
Ancient tropical sea
The rock the cave sits in began to form about 488 million years ago when this part of the world was under a warm, shallow sea. As tiny marine organisms died, their shells fell to the sea floor and built up into massive, hardened limestone layers called Galena dolomite.
About 1-1.5 million years ago, the cave began to form. As rain fell, it filtered through dead plants on the ground, picking up carbon compounds. When combined with water, these compounds became a mild solution of carbonic acid. The acidic water went into the ground, dissolving the limestone by creating fissures. As the carbonic acid dissolved more and more limestone, those cracks grew into passages and whole rooms.
When the water table dropped, oxygen filled the openings. The air helped the dissolved limestone and water solidify, creating the strong walls that keep the passages and rooms from collapsing.
Speleothems – or various rock formations – also formed once air filled the cave. Among them are stalactites, stalagmites, soda straws, flowstone, curtains, lily pads, helictites and oolites. Red and brown formations have a high content of iron oxide while those that are blue or gray contain manganese oxide.
Cephalopod fossil
Fossils also have been found in the cave, most notably a six-foot giant cephalopod, a squid-like creature with a hard shell. That fossils have been found in the cave isn’t surprising; the quarry above the cave was well-known for its fine fossils.
Cephalopods were common in the ancient sea that the cave’s limestone formed in. At that time, Wisconsin sat near the equator, mostly beneath water that was no more a 100 feet deep.
The cave is named for two hills called the Blue Mounds and is in the southern slope of the east hill. In 1987, the cave was named a National Natural Landmark.
When hiking the cave, avoid touching the rock formations, as they are fragile. The cave’s temperature is a constant 50 F regardless of the season, so always wear a sweater or jacket.
An entrance fee is required. Tours run every day of the year except except Thanksgiving and Christmas Eve and Day.
