The Delicate Kansas Chalk Cliffs That Were Once the Bottom of an Ancient Sea

Monument Rocks, Scott City KS

Monument Rocks stands like giant white castles rising from the flat Kansas prairie. These tall formations took shape 80 million years ago when a huge inland sea covered middle America.

Sometime during that period, the Western Interior Seaway split North America into two separate land masses.

The white towers reach up to 70 feet high, and they’re made of Niobrara Chalk, a soft rock formed from seabed mud. This mud built up very slowly, at just 0.036 millimeters each year.

First National Natural Landmark in Kansas

Monument Rocks became Kansas’ first National Natural Landmark on October 31, 1968. The U.S. Department of Interior gave this title because of the rocks’ scientific value.

Each inch of these chalk formations holds about 700 years of Earth’s history. Scientists study them to understand ancient seas and extinct creatures.

In 2008, the site gained more recognition when the Kansas Sampler Foundation named Monument Rocks and nearby Castle Rock as one of the 8 Wonders of Kansas.

The Famous Keyhole Arch

Keyhole Arch draws photographers and visitors from everywhere. This natural window frames perfect views of sky and prairie.

Local stories say the arch began when someone shot at the rocks long ago. A bullet pierced through a thin spot, creating a tiny hole.

Over many years, wind and rain made this hole bigger. People who live nearby have watched it grow throughout their lives.

Scientists believe the arch will keep expanding until it can’t support its own weight. Then the top will collapse, leaving just two chalk pillars.

Marine Fossil Treasures

The white chalk holds countless remains of sea creatures. These animals lived and died when Kansas lay under a vast ocean.

Fossil hunters have found prehistoric fish, turtles, and giant marine reptiles. Mosasaurs and plesiosaurs—huge swimming predators—once hunted here.

Some discoveries show impressive size. Giant clam fossils up to six feet wide have come from these rocks.

Scientists rank this area among the world’s best places to study Cretaceous marine life. The fossils here stayed so well-preserved that tiny details remain visible.

Native American Significance

Several Plains tribes used the land around Monument Rocks for hunting. The Cheyenne, Arapaho, Kiowa, Sioux, and Apache tracked buffalo and other game across these grasslands.

The bright white formations helped them navigate. Standing tall above the flat prairie, the rocks could be seen from miles away.

Tribes also viewed the formations as sacred places. They held spiritual importance beyond their practical use as landmarks.

Evidence of human activity in this area goes back hundreds of years. Many generations of Native peoples lived and traveled through this landscape.

Butterfield Overland Dispatch Trail Landmark

Monument Rocks guided travelers on the Butterfield Overland Dispatch trail during the 1860s. This route began in 1858 after gold was found near Denver.

People rushing to find gold needed a path across the plains. Monument Rocks served as a key waypoint on this journey.

David A. Butterfield started a transport service along this trail in 1865. His company moved goods, mail, and passengers between Kansas and Colorado.

The first stagecoach journey happened in September 1865. One-way passage cost $175—equal to several thousand dollars today.

Fort Monument’s Brief History

The army built Fort Monument in 1865 just a mile from the rock formations. This small outpost protected people traveling on the Butterfield trail.

The route crossed through tribal territories, leading to conflicts. The fort provided safety in this remote, dangerous area.

Unlike major forts, this post had only three basic buildings made mostly from local stone. It operated for just three years before the army abandoned it in 1868.

Today nothing remains of Fort Monument. The prairie has reclaimed all traces of this short-lived military post.

Chalk Formation Process

Monument Rocks began forming when tiny sea creatures died and sank to the ocean floor. Their microscopic shells piled up over millions of years.

This buildup created the Smoky Hill Chalk, part of the larger Niobrara Chalk formation. These chalk beds stretch across western Kansas.

The formations survived because harder rock layers on top protected the soft chalk beneath. This acted like a protective cap against erosion.

Both microscopic shells and larger fossils pack the rock. This mix lets scientists study an entire ancient ecosystem from microscopic plants to large predators.

Wildlife Around the Formations

The prairie around Monument Rocks teems with animal life. Eagles and falcons soar overhead, often perching on the tall spires to hunt.

Mule deer, pronghorn antelope, jackrabbits, and coyotes roam the grasslands. Prairie dog towns dot the landscape, while rattlesnakes hide among rocks and burrows.

Birds of prey use the tall formations as hunting perches. From up high, they scan the prairie for small animals to catch.

These animals form part of the larger prairie ecosystem. Plants, plant-eaters, and predators all depend on each other in this Great Plains habitat.

Continued Erosion and Change

Wind, rain, freezing, and thawing slowly reshape Monument Rocks today. The same forces that carved them continue wearing them down.

The Keyhole Arch shows clear signs of this ongoing change. It grows wider every year as pieces fall away from its edges.

Families living nearby have tracked these changes for generations. Parents show children how the rocks differ from when they were young.

After heavy rainstorms, some locals say the area briefly smells like the ocean. This fleeting scent recalls the sea that created these rocks long ago.

Star Gazing Destination

Far from city lights, Monument Rocks offers amazing night sky views. The dark location lets visitors see stars with exceptional clarity.

On clear nights, stars, planets, and the Milky Way shine brightly overhead. Many sky features invisible in cities appear clearly here.

Star-watchers sometimes gather here for viewing events. The wide-open horizon and minimal light pollution create perfect stargazing conditions.

The white chalk forms create dramatic shapes against the night sky. This stark contrast adds to the magical experience of stargazing in this remote spot.

Visiting Monument Rocks

You can visit Monument Rocks any day during daylight hours. The site sits on private property about 25 miles south of Oakley, Kansas. No entrance fee is required, but respect the owners’ generosity by following all posted rules.

No facilities exist at the site—no restrooms, water, or trash services. Bring what you need and take everything back with you when leaving.

Read More from WhenInYourState.com:

• The 70-Ft-Tall ‘Chalk Pyramids’ in Kansas Are also an Ancient Graveyard for “Sea Dinosaurs”
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