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
The beautiful layers of rock you see here tell a story of the 60-millionyear geologic history of the badlands. From ancient swamps to recent 

coal fires, this landscape is constantly changing. Learn more by 

following the numbered trail posts.

Blue-grey

Bentonite clay is made of ash 

from distant volcanoes.

Brick-red

Clinker forms when coal veins 

catch fire and bake the rock above, 

changing it into this much harder, 

red rock. These fires are a natural 

part of the badlands, and help 

create this fascinating landscape. 

1. Layers 

In this area there was a 12-footthick coal vein deep underground. 

In 1951 it caught fire and burned 

for 26 years. As it burned away, the 

rocks above were left unsupported 

2. Collapse 

Coal Vein Nature Trail

Brown and Tan 

Sandstone, siltstone, and 

mudstone are sediments washed 

down from the Rocky Mountains 

by rivers and streams. 

Black

Coal is the remains of ancient 

plants and animals that lived in 

Everglades-like swamps.

and the surface collapsed, forming 

the depression you are about to 

enter. Before the fire, the land was 

level with the top of the stairs.

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

Stay to the left to follow the posts in numerical order. 
Notice the sediment on either side 

of the trail. Fifty-five 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 five times its weight 

in water. Known as the mineral 

of one thousand uses, it is used to 

seal landfills and ponds, to make 

cat litter, and much more.

3. Bentonite 

Rocks in the badlands are 

generally soft and easily eroded by 

rain and streams. Some are harder 

4. Caprocks 

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

Take the cutoff trail to the right to avoid a section of trail with very 

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

than others, and become caprocks. 

A caprock acts like a hat, shielding 

softer rock underneath. When 

the layers underneath wear away, 

and large pieces of caprock break 

off 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.
Low spots like this one formed 

when the ground collapsed during 

the coal vein fire. They fill with 

water in the wet springtime and 

after summer rains. These seasonal 

ponds are important habitat for 

6. Seasonal Pool 

western chorus frogs that must lay 

their eggs in standing water. 

Listen for the chirping of the male 

chorus frogs near seasonal pools 

from April to June.

Just ahead and to the right is 

where the coal vein fire burned 

out after 26 years (1951-1977). 

Visitors could see smoke, glowing 

coals, and sometimes flames. They 

even roasted marshmallows over 

the fire! 

Right: This photograph was taken 

in the 1970s as the burning coal 

fire crept toward its end.

7. Burn Out 

The dry climate of western North 

Dakota keeps the badlands from 

eroding away 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 

wildflowers you find here, are 

adapted to survival in this land of 

extreme temperatures and little 

moisture.

5. Dry Climate 

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 off sharply. From 

this overlook, you can see how 

plants are affected by the terrain. 

The slopes you see are northfacing. They are cool and shady 

and retain moisture better than 

sunny south-facing slopes. This 

allows juniper and other shrubs to 

thrive. South facing slopes support 

only hardy grasses and a few very 

drought-tolerant shrubs. 

Feel the red rock next to the post. 

It locally called scoria, but more 

correctly called clinker. It is one of 

the hardest rocks in the badlands. 

Clinker is created when a burning 

coal seam bakes the rock layer 

above it. Baking rock is like putting 

clay into a kiln to make pottery 

— the rock hardens as it bakes. 

Look for clinker functioning as a 

caprock atop buttes throughout 

the park.

9. Clinker 

Just ahead, stairs lead to the valley 

of a seasonal stream. As you 

descend, notice the cool, moist air 

against your skin. This stream bed 

is dry most of the year. It usually 

runs only during spring snowmelt 

and summer rainstorms. 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 differences?

10. Seasonal Stream 

Continue straight ahead to follow the guided nature trail.
This is the spot where the coal vein 

ignited during a lightning storm 

in 1951. Even today, these natural 

fires can be started by lightning, 

prairie fires, or even spontaneous 

combustion.

11. Ignition 

The small spur trail going up 

the hill leads to an overlook. Be 

careful; the edge drops sharply. 

When you look to the left and 

right you can see and feel the 

clinker where it forms a protective 

12. Clinker Overlook 

caprock. The red color of the 

clinker comes from iron in the 

rocks that oxidized (rusted) 

when the rock was baked by the 

underlying coal fire.

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, the 

ground became unstable, causing 

13. Slumping 

cracks in the hillside. Rain flowing 

into the cracks weakens the hill 

more, especially where it comes in 

contact with bentonite layers that 

become slippery when wet. As the 

wet bentonite slides, the hill slowly 

slumps away.

Caution! Steep cliff edges ahead. 
June 1958

When the underground coal fire 

was burning, this area looked 

more like a wasteland than a 

grassland. After the fire 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 different species of grasses 

and other plants. 

14. Grassland 

Take in the view. The things you 

have observed on this trail are 

not unique to this one spot. They 

can be seen, felt, and identified 

throughout the badlands. Even 

today, coal fires shape the dynamic 

landscape of the badlands. 

Geology is not only a study of 

the past; here it is an ever present 

process. How do these things fit 

into the big picture of the park? 

How long will these processes 

continue to shape this land? 

15. The Big Picture 
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 fire burned deep into the 

hillside, cracks in the rock layers 

allowed air to be sucked down 

into the fire. Fire burned up the 

cracks and baked the rocks nearby 

forming vertical “chimneys.” 

Chimneys are the hottest part of 

the coal fire 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.

16. Chimney 

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 interpretation rangers of 

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

Thank you for your support!

EXPERIENCE YOUR AMERICATM

There are many signs that large coal vein fires have burned throughout 

the park in the past. Even today, coal fires 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.