Missouri is known as the Cave State, but it also has its share of another geologic wonder — natural bridges and tunnels.

Missouri is known as the Cave State, but it also has its share of another geologic wonder — natural bridges and tunnels.

The massive formations are featured at four state parks — Bennett Spring, Grand Gulf, Ha Ha Tonka and, of course, Rock Bridge Memorial.

Natural bridges may be the remains of a cave that collapsed, with only a portion of the ceiling still standing. But while the entrance to caves can be mysterious, even foreboding, natural bridges are more inviting with the light at the end of the tunnel beckoning a visitor to come on in and explore.

Jay Wilbur is retired and lives in Texas, but he’s familiar with Missouri as the co-founder of the Natural Arch and Bridge Society. The group has some 150 members who share a passion for arches, bridges and tunnels and travel all of the country, even the world, to visit a new one.  The group’s website, naturalarches.org, lists 29 significant formations in Missouri.

“Missouri would definitely be in the top 10 among states for number of arches, bridges and tunnels,” Wilbur said. “The book ‘Geologic Wonders and Curiosities of Missouri’ is a really respected publication. It was the first to come out and set a precedent for other states.”

The book was written by the late Thomas R. Beveridge and published in 1978 by the Missouri Department of Natural Resources’ Division of Geology and Land Survey. It was revised in 1991 by Jerry Vineyard . The book catalogues 85 arches, bridges and tunnels and describes a total of 457 geologic features, including mountains, hills, knobs, mounds, shut-ins, waterfalls and rapids.

The book is available on-line at the Missouri Geology Store, operated by the Division of Geology and Land Survey. Visit missourigeologystore.com.

A sense of wonderment

While natural bridges may have been formed the same way, they each have their own personality.

Bennett Spring State Park, near Lebanon, is known for another geologic marvel, its namesake spring that feeds one of Missouri’s popular trout streams. The Natural Tunnel Trail begins at a parking lot near the spring and heads 7.5 miles, round trip, into the woods to a tunnel that is 296 feet long and forms an S curve through a hill.

Grand Gulf State Park, on the Arkansas border near Thayer in south-central Missouri, is known as the “Little Grand Canyon of the Ozarks.” Deeper that is it wide, the sheer rock walls drop some 130 feet, revealing the remnants of a cave that collapsed some 10,000 years ago. A mile-long canyon leads through a 250-foot-long natural bridge.  The Natural Bridge Trail leads visitors over the natural bridge and offers a glimpse into the spectacular Grand Gulf below. 

Ha Ha Tonka State Park, near Camdenton at the Lake of the Ozarks, is chock full of geologic wonders, including a natural bridge that spans 60 feet, is 100 feet high and 70 feet wide. It can be reached by a short walk from a parking lot, or on the Colosseum Trail, which also shows off the 150-foot deep Colosseum Sinkhole. At one time, a road passed over the bridge.

Rock Bridge Memorial State Park near Columbia is named for a massive limestone tunnel with a stream flowing through it. A boardwalk leads from the tunnel to the nearby Devil’s Icebox, a collapsed sinkhole with an entrance to a cave system.

Wilbur said all the formations have something in common — a sense of wonderment.

“They’re just unusual, interesting and very aesthetically pleasing things,” he said.

Missouri’s first arch

So, what’s the difference between a natural arch, bridge or tunnel? The answer is, not much. All are holes cut through rock by erosive forces. Bridges and tunnels usually have a stream running through them.

In Missouri, the formations are found in the karst topography of the Ozarks, where mildly acidic groundwater moves through soluble bedrock, dissolving the limestone and dolomite into a subterranean maze of caves and fissures. The result is a Swiss-cheese landscape of sinkholes, springs and caves, which sometimes collapse and leave a bridge or tunnel standing.

Wilbur said the state parks preserve four of Missouri’s largest natural tunnels or bridges, but pointed out yet another park with a significant geologic oddity.

Hikers and bikers on Katy Trail State Park can find this treasure at mile marker 166.9, between McBaine and Easley south of Columbia. An exhibit points up to Pierced Rock, a hole about 25-feet high and 15-feet wide cut in the rock high up on the bluff. The French name is Roche Percee.

“That is historically a very important arch,” Wilbur said. “It’s not big or spectacular, but it was actually noted by the Lewis and Clark Expedition. It’s the first arch in Missouri to be documented.”

A bike ride along the Missouri River takes you to Pierced Rock. The natural bridges at Grand Gulf, Ha Ha Tonka and Rock Bridge Memorial are at the end of short walks. Getting to the bridge at Bennett Spring requires a four-hour hike. But that’s part of the fun of exploring natural bridges and tunnels, Wilbur said.

“They get you outside into nature, they usually involve some kind of challenge to get to,” he said. “Once you’re there, you have something fascinating to appreciate.  We like to say it’s the icing on the cake.”