NEAR VERMILLION, S.D. (KTIV) - It’s been more than 217 years since the Lewis and Clark expedition charted a course through Siouxland on the Missouri River.

On Aug. 20, 1804, they buried Sergeant Charles Floyd on the banks of the Missouri River in what’s now Sioux City.

Five days later near what’s now Vermillion, South Dakota they battled the heat to explore a massive hill feared by the native Americans as a “mountain of evil spirits.” It’s a hill now known as “Spirit Mound.”

Spirit Mound is a place where you can literally walk in the footsteps of Lewis and Clark.

These days it is a little less than a mile from the parking lot to the top of Spirit Mound north of Vermillion.

It was a longer slog through the tall grasses on that hot August day as Lewis and Clark went to see if the stories they’d heard were true.

“They heard that there were little devils that lived in the hill,” said Meghann Jarchow of the Spirit Mound Trust. “And so these eighteen-inch people with big heads who lived in the hill. And if you climbed the hill they would shoot you with these poison arrows that might kill you.”

Jarchow is president of the Spirit Mound Trust and a professor at the University of South Dakota with a background in prairie ecology.

“They walked up this way and were sort of amazed at what they saw,” she said.

What they saw wasn’t the little devils they’d heard about.

“And then there’s the entry of, it’s the most beautiful landscape. They saw hundreds of bison and elk grazing,” explained Jarchow.

It was a sea of buffalo.

They also noted the abundance of insects near the top which attracted great flocks of swallows.

The captains speculated it was the birds that gave the mound its air of mystery.

What created this magnificent mound on the prairie? It was the last glacier 20,000 years ago that covered the northern U.S.

“And so you can image two miles of glaciers advancing and retreating, advancing and retreating, it ground up the soil. And for whatever reason it didn’t ground up the mound,” said Jarchow.

And millions of years before that it was covered by the sea.

“Like when you climb right before the summit there’s some yellowish rock that’s chalk. You know so it’s an example of back when we were under an ocean during the dinosaur age, it’s chalk from the dead bodies of the sea animals that lived there,” Jarchow continued.

An ice jam that led to massive flooding on the Missouri River in 1881 also changed the course of the river, moving it miles away from where Lewis and Clark started their trek to Spirit Mound.

“Well, I think more like ten-ish. I mean it’s a significant jump,” according to Jarchow.

In 1986 the Spirit Mound Trust was created to save the mound and its 320 acres as a restored prairie and public place.

“That is the major goal of the park of Spirit Mound, to try and recreate what it might have looked like,” emphasized Jarchow.

The Spirit Mound Trust was founded by some local citizens in 1986 to preserve and restore Spirit Mound, which is now the only state park in Clay County, South Dakota.