Watch CBS News

Finding Minnesota: Mystery Cave

MINNEAPOLIS (WCCO) -- Southeastern Minnesota is a landscape filled with scenic views.

At Forestville/Mystery Cave State Park, visitors can see bluffs, forests and streams. But one of the park's biggest attractions is below the earth's surface.

"We've got lots of lovely cave formations," Mary Gustafson, a Department of Natural Resources interpretive naturalist at Mystery Cave, said.

It is a natural labyrinth of limestone spread out over 13 miles. The underground cavity grew over millions of years, each time the nearby creek flooded.

"This cave was found in 1937 by a gentleman named Joe Petty, and he was walking along the river outside the cave," Gustafson said. "As far as we know, he's the first human to get inside Mystery Cave."

Fast forward nearly 80 years and Mystery Cave now attracts thousands of visitors each year who show up to see a piece of Minnesota's history.

"It's a window into the past and can tell you what was going on in Minnesota long before there were people to write down what was happening," Gustafson said.

As an interpretive naturalist for the DNR, Mary Gustafson is a tour guide who helps makes sense of the cave's intricacies.

"Personally, I love it and I love getting to talk to people about it and have them think about it," she said.

The majority of the cave is made of limestone, and its porous walls tell of an ocean once covering the state. Gustafson says the rock is so old that it predates the Jurassic period.

"The rocks themselves, when we look at shells and limestone, there are creatures that went extinct 450 million years ago," Gustafson said. "Four-hundred-and-fifty million years is twice as old as the very first dinosaur."

Every formation shows the impact of water if given time. In certain areas of the cave, stalactites slowly grow with every drip. Some are just inches tall, others are several feet.

"On average, one of the stalactites will grow a tenth of a millimeter in a year, about the thickness of your fingernail," Gustafson said.

In other areas, the continuous trickle of water carves away at the limestone, leaving its place into the cave's story.

"There's always something new, some detail I haven't noticed," Gustafson said.

Without the interference of nature's elements, like wind or rain, minerals take shape in ways rarely seen above ground.

Water can stay so still that a rock formation called shelf stone will eventually form on a pool of water.

"Shelf stone is something that forms in pools of water. We had a pool of water and, as carbon dioxide escaped off the surface, we had thin tissue paper sheets of minerals at the surface," Gustafson said.

Not far from the shelf stone sits another formation that has become the focal point of the cave tour.

Turquoise Lake is a subterranean body of water that appears to be a brilliant shade of blue.

"The color is because there's dissolved calcium carbonite minerals in the water," Gustafson said. "When you dissolve calcium carbonite you get a reflection of the blue and blue green light to your eyes so it appears tropical blue."

It is a natural preservation of Minnesota's past, sitting just below the earth's surface.

Mystery Cave offers several different tours, including one at night and another that takes visitors through undeveloped areas of the cave. Click here to learn more.

Send us your Finding Minnesota ideas here.

View CBS News In
CBS News App Open
Chrome Safari Continue
Be the first to know
Get browser notifications for breaking news, live events, and exclusive reporting.