Be aware of the following: 

Coal Vein 

A Guided Nature Trail 

National Park Service 

U.S. Department of the Interior 

Theodore Roosevelt National Park 

Cliff Edges Stairs Rattlesnakes Wildlife Poison Ivy 

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Beautiful layers of rock tell a story of the 60-million-year geologic history of the 

badlands. From ancient swamps to recent coal fres, this landscape is constantly 

changing. Learn about badlands geology by following the numbered trail posts. 

Stay to the left to follow the posts in numerical order. 

1. Layers

Each layer of rock has its own origin story, told by its color. 

Brick-red Black 

Clinker forms when coal veins catch Coal is the remains of ancient plants 

fre and bake the rock above, changing and animals that lived in Evergladesit into this much harder, red rock. like swamps. 

Brown and Tan Blue-grey 

Sandstone, siltstone, and mudstone Bentonite clay is made of ash from 

are sediments washed down from the distant volcanoes. 

Rocky Mountains. 

2. Collapse

In this area there was a 12-foot-thick were left unsupported and the surface 

coal vein deep underground. In 1951 collapsed, forming the depression you 

it caught fre and burned for 26 years. are about to enter. Before the fre, the 

As it burned away, the rocks above land was level with the top of the stairs. 
 

 

3. Bentonite 

Notice the sediment on either side of 

the trail. Fifty-fve million years ago, 

volcanoes in the Rockies spewed out 

ash that blew east. At that time, this 

area was a vast, tropical swamp. The 

ash settled in wet areas and became 

bentonite clay. 

Bentonite looks like popcorn when 

dry (below), but becomes sticky, slick 

mud when wet. It can absorb up to fve 

times its weight in water. Known as the 

mineral of one thousand uses, it is used 

to seal landflls and ponds, to make cat 

litter, and much more. 

Stay to the left to continue on the guided nature trail. 

Take the right on the cutoff trail to avoid a section of trail with very steep stairs. 

You will rejoin the guided nature trail near post #11. 

4. Caprocks 

Rocks in the badlands are generally 

soft and easily eroded by rain and 

streams. Some are harder than others, 

and become caprocks. A caprock 

acts like a helmet, shielding softer 

rock underneath. When the rocks 

underneath fnally erode away, large 

pieces of caprock break of and fall. 

The large pieces of sandstone behind 

you were once caprocks at the top of 

the hill. 

Left: An example of a caprock found 

elsewhere in the park. 
 

 

5. Dry Climate 

The dry climate of western North 

Dakota keeps the badlands from 

eroding away more quickly — if rain 

were more common, the soft rocks 

would have washed away long ago. 

The lack of moisture allows only the 

hardiest plants to survive. 

The trees here are Rocky Mountain 

juniper. They, and all the other shrubs, 

grasses, and wildfowers you fnd here, 

are adapted to survive in this land 

of extreme temperatures and little 

moisture. 

6. Seasonal Pool 

Low spots like this one formed when 

the ground collapsed during the coal 

vein fre. They fll with water in the wet 

springtime and after summer rains. 

These seasonal ponds are important 

habitats for western chorus frogs which 

must lay their eggs in standing water. 

Listen for the chirping of the male 

chorus frogs near seasonal pools from 

April to June. 

7. Burn Out 

Just ahead and to the right is where the 

coal vein fre burned out after 26 years 

(1951-1977). Visitors could see smoke, 

glowing coals, and sometimes fames. 

They even roasted marshmallows over 

the fre! 

Right: This photograph was taken in 

the 1970s as the burning coal fre crept 

toward its end. 

Caution! Steep cliff edges ahead. 
 

 

 

 

8. Hills Overlook 

The trail goes to the right. To your left is 

an overlook. Be careful; the edge drops 

of sharply. From the overlook, you can 

see how the terrain afects plant life. 

The slopes you see face north. They 

receive very little direct sunlight which 

helps retain moisture, allowing juniper 

to thrive. South-facing slopes receive a 

lot of direct sunlight. They are very dry 

and support only hardy grasses and a 

few drought-tolerant shrubs. 

9. Clinker 

Feel the red rock next to the post. It is into a kiln to make pottery — the rock 

locally called scoria, but its true name hardens as it bakes. Because clinker 

is clinker. Clinker is created when a is one of the hardest rocks in the 

burning coal seam bakes the rock layer badlands, it functions as a caprock atop 

above it. Baking rock is like putting clay many buttes. 

10. Seasonal Stream 

Just ahead, stairs lead to the valley of 

a seasonal stream. As you descend, 

notice the cool, moist air against your 

skin. Because it is protected from the 

sun, this area stays moist and cool. 

Note the plants you see here and 

compare them to the plants you have 

encountered in open grassland. What 

are the diferences? 

Continue straight ahead to follow the guided nature trail. 

11. Ignition 

This is the spot where the coal vein can be started by lightning, prairie fres, 

ignited during a lightning storm in or even spontaneous combustion. 

1951. Even today, these natural fres 

Caution! Steep cliff edges ahead. 
 

 

12. Clinker Overlook 

The small spur trail going up the hill the clinker where it forms a protective 

leads to an overlook. Be careful; the caprock. The red color of the clinker 

edge drops sharply. When you look to comes from iron in the rocks that has 

the left and right you can see and feel oxidized (rusted). 

13. Slumping 

The hill in front of you has the 

appearance of sliding slowly into a 

jumble. That is exactly what it is doing 

through a process called slumping. 

When the coal vein burned under this 

area, cracks formed in the hillside. 

Rain fowing into the cracks weakens 

the hill, especially where it saturates 

bentonite clay layers which become 

slippery when wet. As the bentonite 

slides, the hill slowly slumps away. 

Slumping happens on a small scale like 

you see here, but also on a very large 

scale when entire hillsides slide. The 

picture below, taken in the North Unit, 

shows masses of rock that slid from 

near the top of the canyon, coming to 

rest far below. 
 

 

June 1958 

14. Grassland 

When the underground coal fre was 

burning, this area looked more like 

a wasteland than a grassland. After 

the fre burned out, prairie plants 

reclaimed the land slowly over time. 

From a distance, prairie may look plain, 

but it is actually one of the most diverse 

ecosystems in the world. An up-close 

look reveals many diferent species of 

grasses and other plants. 

15. The Big Picture 

Take in the view. The things you have Geology is not only a study of the past; 

observed on this trail are not unique here it is an ever present process. How 

to this one spot. They can be seen, do these things ft into the big picture 

felt, and identifed throughout the of the park? How long will these 

badlands. Even today, coal fres shape processes continue to shape this land? 

the dynamic landscape of the badlands. 
16. Chimney 

What is unusual about the massive 

piece of clinker in front of you? 

Fires need oxygen, even when they are 

burning underground. As the coal fre 

burned deep into the hillside, cracks in 

the rock layers allowed air to be sucked 

down into the fre. Fire burned up the 

cracks and baked the rocks nearby 

forming vertical “chimneys.” Chimneys 

are the hottest part of the coal fre and 

bake the rock inside into a very hard 

clinker called porcellanite which is 

especially resistant to erosion. 

This chimney you are looking at was 

exposed when softer sediments around 

it eroded away. 

There are many signs that large coal vein fres have burned throughout the park in 

the past. Even today, coal fres can sometimes be found shaping and changing the 

landscape of the badlands. 

Geology is not only a study of the past; it is an ongoing process. 

We hope you enjoyed your hiking experience. 

Please return this brochure to the box at the beginning of the trail. Thank you! 

This trail brochure was written and produced by the rangers of 

Theodore Roosevelt National Park. It was printed using your fee dollars. 

Thank you for your support! 

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