Junior Explorer

Discover the Malm Gulch

Petrified Forest 

U.S. Department of the Interior • Bureau of Land Management
¬

Challis

Malm Gulch

Salmon River

Twin

Peaks

Caldera

75

Custer

Graben

Salm

o

n

River

93

2 miles to trailhead

0.7 miles

0.4 miles

Interpretive sign

Interpretive sign Petrified forest

Trailhead

75

Salmon

River

Malm Gulch

North

Montana

Canada

Wyoming

Nevada Utah

Oregon Washington

BLM Idaho’s

Challis

Field Office

BLM-administered lands

Forest Service

State

Private

Vinegar

Baking

Soda

•	 Only vehicles with four-wheel drive 

and high clearance are recommended. 

•	 The road to the trailhead is not 

maintained and frequently

washes out. 

•	 Use caution when heavy rainfall 

occurs, as severe thunderstorms can 

cause flash floods.
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Table of Contents

Welcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

What Are Public Lands? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Activity 1: Growth Speed of Giant Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Activity 2: A Different Time, A Different Place . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Activity 3: Geological Activity Reshapes Our Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Activity 4: Colorful Ash Cultivates Unique Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Activity 5: Undercover Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Activity 6: Volcanoes Aid Mineral Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Activity 7: Rock Layer Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Activity 8: Petrification Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Activity 9: What Am I? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Activity 10: A-Mazing Volcanoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Bonus Activity: Make Your Own Volcano . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Junior Explorer Pledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Answer Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
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Welcome

Hello Junior Explorer!

Are you ready for an adventure? In 

this activity book, you will explore 

the Malm Gulch area. It is a petrified 

forest located about 10 miles south of 

Challis, Idaho. Fifty million years ago, 

this area of Idaho was much different. 

The climate was cool and wet, just like 

you see now on the Pacific coast. Large 

sequoia or redwood forests covered 

the mountains, and ferns blanketed 

the forest floor. All of that changed 

when geological activity in the area 

increased. Violent volcanic eruptions 

showered the area with volcanic ash, 

changing the environment and turning 

trees into a vast petrified forest. All that 

remains of these forests today are a 

few tree stumps—some almost 6 feet 

in diameter—in the Malm Gulch area. 

As you trek along the short Malm Gulch 

hiking trail, try to imagine this dry area 

covered with giant trees and lush ferns. 

Today, the area is managed by the 

Bureau of Land Management (BLM) 

Challis Field Office. The BLM installed 

fences in the 1970s to protect the last 

examples of this ancient petrified forest 

from vandalism. Please enjoy these 

last remnants, but do not harm them. 

Leave them as they are so others can 

appreciate them too. 

Earn your Junior Explorer award and 

certificate by visiting the Malm Gulch 

area. Do this on a weekend afternoon 

with your family or maybe on a field trip 

with your class. Once you have 

completed at least 7 of the 10 activities 

in this book, you are on your way to 

protecting America’s public lands and 

becoming a Junior Explorer for the 

Malm Gulch area. Then, say the 

pledge at the end of this book. Sign 

the certificate, and bring or mail it to 

the BLM.

If sending the certificate by mail, send 

to the following address:

Bureau of Land Management

Challis Field Office

1151 Blue Mountain Rd.

Challis, ID 83226

Nature is a great place to learn as long 

as you know how to be kind and safe. 

During your adventure, remember the 

following tips.

Be Kind to Nature: If you see a wild 

animal, stay quiet, and watch it from 

a distance. Take binoculars if you 

can. That way you can watch animals 

closely without disturbing them. If you 

see or have any trash, be sure to pick it 

up and pack it out in your backpack.

Explore the Outdoors Safely: Before 

setting off on your journey, bring your 

water bottle with you. Your adventure 

may be hot and dry at certain times

of the year, and there is no water 

onsite. Also, watch your footing

since the trails in this area are

rocky and uneven. Wear good shoes

or boots that will support and protect 

your feet and ankles. Lastly, look out

for rattlesnakes, which are

occasionally seen in the area.

Leave What You Find:

The remaining

petrified trees within

Malm Gulch can never be

replaced. If they are

damaged, they will be gone

forever. Enjoy looking at these 

treasures, but please be respectful 

and leave everything as you find it for 

others to enjoy. If you’re

careful now, more

Junior Explorers like

you can see and learn

about the area.
3

What are Public Lands?

Public lands are set aside for everyone to use! The BLM manages more than 

245 million acres of public land, mostly in the West. Public lands are located in 

many types of environments, such as forests, mountains, deserts, grasslands, 

tundra, lakes, and rivers.

Many different activities happen on public lands. Sometimes wild horses live 

on these lands. Sometimes oil, coal, and other minerals come from these 

lands. Sometimes historical landmarks are taken care of on these lands. And 

often, people enjoy outdoor activities on these lands, such as camping, hiking, 

mountain biking, fishing, rock climbing, horseback riding, and boating.

Since public lands are available for everyone, we must use the lands 

responsibly and be good stewards. We all have to work together to take care 

of the land so that future Junior Explorers can enjoy it too.

BLM-managed lands
4

Growth Speed 

of Giant Trees 

Activity 1:

Scientists have identified the large petrified 

tree stumps in the Malm Gulch area as 

redwood or sequoia trees. Today, the largest 

concentration of redwood trees in the United 

States lives in California. The California 

redwoods remain some of the tallest and 

oldest living trees in the world. The petrified 

trunks of the trees in Malm Gulch indicate 

that some were more than 6 feet in diameter, 

much larger than trees in this area today.

The average person 

reaches their full height 

around 19 years old. If the 

trees in the Malm Gulch 

area were about 300 feet 

tall, and if the trees grew 

an average 2 feet taller 

each year, how long did it 

take for the trees to reach 

their full height? 

Answer: _________________
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A Different 

Time,

A Different 

Place 

Fifty million years 

ago, the scene in 

Malm Gulch was 

very different than 

today. Central Idaho 

had a much warmer 

and wetter climate 

than it does now. 

Today, the Cascade 

mountain range 

blocks much of 

the warm, moist 

air coming from 

the Pacific Ocean. 

Fifty million years 

ago, the Cascade 

mountain range did 

not even exist. The 

giant trees at Malm 

Gulch needed the 

warmer, moister air 

to grow and survive. 

Connect the dots 

to determine what 

this area might have 

looked like millions 

of years ago. Then 

color it! 

Activity 2:
6

Geological 

Activity 

Reshapes

Our Earth

Activity 3:

In 1980, a volcano called 

Mount St. Helens erupted 

in Washington State. About 

48 million years ago, in the 

Challis area, geologists think 

at least six volcanic eruptions 

were hundreds of times more 

powerful than the Mount St. 

Helens’ eruption. Two types of 

volcanic eruptions happened 

in the Challis area. First, sheets 

and rivers of molten rock called 

lava erupted from volcanic 

vents (cracks and holes in the 

earth). Later, multiple volcanic 

eruptions sent up clouds of 

hot gas, ash, and pumice that 

covered the entire area. Today, 

people see the white and pastelcolored soils and rocks in the 

Malm Gulch area, which are 

remnants of the ash deposits. 

The heat of the eruptions 

destroyed most of the trees in 

the Malm Gulch forest. However, 

volcanic ash buried some trees 

that eventually became the 

petrified logs you see today. 

Draw a picture of what this 

eruption might have looked like. 

Don’t forget to show the giant 

trees—some were buried and 

others burned up!
7

Activity 4:

Colorful Ash 

Cultivates 

Unique 

Growth

The pastel-colored hills 

(pale greens, pinks, and 

yellows) that dominate 

the Malm Gulch area tell 

of a time long ago when 

volcanic ash engulfed this 

area. Very few plants live 

in these soils because 

the soils are powdery, 

very crumbly, and easily 

eroded. In spite of these 

challenges, some plants 

have adapted to this 

harsh environment. The 

Challis milkvetch, Challis 

crazyweed, and wavyleaf 

thelypody include some 

of the plants unique to the 

area. In the puzzle, find the 

names of plants that grow 

in the Malm Gulch area. 

CRAZYWEED

MILKVETCH

SAGEBRUSH

GREASEWOOD

PAINTBRUSH

SUNRAY

RABBITBRUSH

WILDRYE

HAWKSBEARD

PENSTEMON

THELYPODY

RICEGRASS

LAVA ASTER

PHACELIA

WHEATGRASS

O N J A Y L L Q P Z W A P Y M U B S W U

R R H Z F J I H O H G B A G L C K V X K

S E N M D M A P E A H W I E Y R D L I W

H Y T W S C K A U Q M R N V F C Y W X V

L A K S E A T H X D H Z T Y C C P U R H

V G W L A G G F I S W U B A Z X V O H K

U X I K R A G E U W Z U R M U P F W C W

T A Q A S U V R B P L L U D V F A H T Z

G P S L Z B B A G R E A S E W O O D E C

Y S D W W T E M L N U Y H K O P N F V U

F X R O I P B A O S P S N L F K O H K D

J O S B S E Q M R H X J H D S Z I A L T

Z P B J K O E Z D D E E W Y Z A R C I H

L A V K G T G B U E N F S L V I R Y M E

R O Z M S N A C Y C S X Y V O A H E H L

V F P N S P Z J P D P V N A V F D I H Y

M Q E R I C E G R A S S G P R S Q I I P

W P Q D R R T K F D I G M F S N K B T O

S W T T P R G V A Z U T T N G P U Y Y D

G X J W X Z H V J W A Q A A L Y P S S Y
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1. After the volcanoes covered the Malm Gulch area with volcanic 

ash and pumice, a very ______________ process began. This 

process is called _______________________. Erosion is caused by 

many different factors, including wind, water, ice, and gravity. 

2. First, ________________________ gradually broke down and 

loosened the soil and rock covering Malm Gulch. The loose soil 

and rock was then transported by __________________ rolling 

down the mountain. This loose material is called sediment. 

3. The sediment was eventually transported to other locations 

or washed down into ________________________ and 

______________________. 

4. Sometimes, abrupt movement of large amounts of soil and 

rock from higher elevations to lower elevations occurred, 

which is called a _____________________________________. 

5. Over time, this erosion and weathering uncovered the 

______________________________ trees you see today in the 

Malm Gulch area.

1 = P

2 = D

3 = E

4 = S

5 = O 

6 = W 

7 = T

8 = N

9 = I

10 = L

11 = A

12 = H

13 = R

14 = V

15 = M

16 = F

4 - 10 - 5 - 6

3 - 13 - 5 - 4 - 9 - 5 - 8

6 - 3 - 11 - 7 - 12 - 3 - 13

6 - 11 - 7 - 3 - 13

4 - 7 - 13 - 3 - 11 - 15- 4

13 - 9 - 14 - 3 - 13 - 4

10 - 11 - 8 - 2 - 4 - 10 - 9 - 2 - 3

1 - 3 - 7 - 13 - 9 - 16 - 9 - 3 - 2

Volcanic ash buried the tree stumps at Malm Gulch 

about 48 million years ago. Why do you think we 

can see these tree stumps now? To learn how they 

were uncovered, decode the message by using your 

detective skills and the secret code. 

Activity 5: 

Undercover 

Work
9

Gather the following materials:

► salt

► sugar

► two clear plastic cups

► hot water

► small circles of cardboard to cover cups

► spoon

Instructions:

1. Pour about 2 inches of hot water into a cup.

2. Stir sugar into the water until no more will dissolve. This 

may take a while. Keep doing this until you’re sure no more 

will dissolve.

3. Do the same with another cup of hot water. This time add 

salt until no more will dissolve.

4. Cover each cup with a piece of cardboard, and set them in a 

place away from heaters, direct sunlight, drafts, or anything 

else that could cause the temperature to change.

5. Leave the cups in a safe place where they will be 

undisturbed for several days.

6. When the crystals are large enough to clearly see their 

shapes, remove a few. You may want to use a magnifying 

glass to see the crystals even better. Notice the shape of 

the entire crystal and also the shape of individual flat sides.

Because of past volcanic activity in this area, the area is rich in 

minerals. Molten rock deep in the earth (called magma) heated

water deep beneath the earth’s surface. Hot water holds many more 

elements than cold water. The mineral-rich hot water rose to the 

surface. As the water cooled, the different minerals crystallized. 

Prehistoric people used glasslike volcanic rocks, like obsidian and 

fine-grained basalt to make tools, knives, spears, and arrowheads. 

Today, as in the past, miners search for minerals in this area. Besides 

well-known minerals like gold and silver, miners can find dozens of 

different kinds of gemstones in Idaho, such as agate, garnet, opal, and 

topaz. The elements in a mineral cause its crystals to grow in 

specific shapes. Some look like cubes, tilted boxes, or long thin 

fibers. Grow your own crystals by conducting the experiment 

described below.

Volcanoes 

Aid Mineral 

Creation

Draw a sugar crystal. 

How are they different?

Activity 6: 

How are they similar?

Draw a salt crystal. 
10

3

1

1Oldest

Oldest

Youngest

Youngest

2

3

4

1

2

5

4

4

7

6

Activity 7: 

Based on what you’ve learned about geologic layers,

list the layers in order from youngest to oldest for Diagrams 3 and 4.

Rock Layer 

Formation

After you visit the trees in Malm Gulch, drive toward Challis along 

Highway 75. If you look closely, you will see examples of folding in 

the rocks that form the river canyon. These rocks show geologists 

where ancient mountain-building events occurred. Generally, 

rock layers are deposited in flat layers. But when geologic events 

occur, such as volcanic eruptions or earthquakes, those flat rock 

layers can become folded or tilted. Rock layers can also be eroded 

to form caves or canyons. Younger layers of rock may also cut 

through or intrude into one or more layers of older rock.

Diagrams 1 and 2 

demonstrate the

oldest and youngest 

layers of rock.

Study these diagrams.

Diagram 1

Diagram 3

_________________

Youngest

_________________

_________________

_________________

_________________

_________________

Oldest

Diagram 4

_________________

Youngest

_________________

_________________

_________________

_________________

_________________

_________________

_________________

_________________

_________________

_________________

Oldest

Diagram 2

C

F

F

D

A

E

B

L

H

H

F

M

M

A

G

K

C

D

C C

B B

J J
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Activity 8:

Petrification 

Process

The trees in the Malm 

Gulch area became 

petrified. Petrified 

means the remains of 

the wood turned into a 

fossil or stony material. 

Very specific steps must 

happen for wood to 

become petrified. First, 

volcanic ash covered 

the trees at Malm Gulch. 

The ash contained 

a high amount of an 

element called silica. 

As time passed, the 

trees’ cells degraded or 

dissolved. As the silica 

in the ash was dissolved 

in water, it slowly filled 

spaces in the tree 

where cells had once 

been. Slowly over time 

(thousands of years), the 

trees became petrified.

Based on the highlighted 

words in this paragraph 

and previous knowledge 

you learned in this 

activity book, complete 

the crossword puzzle.

Across

2. Volcanic ash contains a high amount of an element called 

___________.

4. Over time, the trees’ __________ degraded or dissolved. 

(see page 9 for a hint.)

7. Agate, opal, and topaz are types of ____________. (See page 9 for a hint.)

8. Erosion is a very _____ process. (See page 8 for a hint.)

9. The state in which Malm Gulch is located. ____________

(See page 2 for a hint.)

Down

1. Volcanic pumice and _____ once covered the trees in Malm Gulch.

3. Millions of years ago, the ___________ of Idaho was warmer and 

wetter. (See page 5 for a hint.)

4. The chemical elements in a mineral cause its ____________ to grow 

in specific shapes. (See page 9 for a hint.)

5. When wood is fossilized or turned to stone, it is called 

_____________________.

6. Because Idaho is rich in minerals, _______________ can find dozens 

of different gemstones. (See page 9 for a hint.)

1

2 3 4

8

7

9

5 6
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What 

Am I?

You have learned a lot about the Malm Gulch 

area. You have specifically learned about the 

petrified tree stumps, rock layers, minerals, 

and volcanic activity. Now, unscramble the 

words based on the following clues.

1. I am, possibly, the type of tree that used to grow in the Malm Gulch 

area.

I am also one of the oldest and tallest tree types in the world.

W D O O E R D ___ ___ ___ ___ ___ ___ ___

2. When I erupt, I release hot gas, ash, and pumice.

I can also release sheets of molten rock called lava.

C O N V O A L ___ ___ ___ ___ ___ ___ ___

3. When chemical elements combine, I am made.

I become rich in the earth because of volcanic activity.

E R L A M I N ___ ___ ___ ___ ___ ___ ___

4. I happen over time as a result of wind, water, ice, and gravity.

Because of me, the petrified trees at Malm Gulch were uncovered.

R E O S N I O ___ ___ ___ ___ ___ ___ ___

5. I am the study of the earth and rocks and how they change.

People that study me often become geologists.

G L O E O Y G ___ ___ ___ ___ ___ ___ ___

?

Activity 9: 
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Activity 10: 

A-Mazing 

Volcanoes

As you can see, the Malm Gulch area 

has changed significantly over time. 

Help this Junior Explorer travel in time, 

from 50 million years ago back to the 

21st century. Watch out for the lava 

and the deep ash deposits!
14

Cooking

Oil

Flour

Salt

Baking

Soda

Baking Dish

+

Bonus Activity: Make Your 

Own Volcano

The Twin Peaks caldera, west of Challis, is roughly 121⁄2 miles 

in diameter. Although the caldera was not the source of the 

volcanic ash in Malm Gulch, the Twin Peaks caldera is a very 

visible example of volcanic activity in this area. Now that you 

have learned a little about volcanic activity, you can build your 

own volcano! This baking soda and vinegar volcano is a simple 

science experiment that mimics a real volcano. You can do this 

experiment outside, or ask permission to do your experiment 

inside. Ask an adult to help. Expect the experiment to take about 

30 minutes to complete.

What You Need:

6 cups of flour

2 cups of salt

4 tablespoons of cooking oil

2 tablespoons of baking soda

warm water

plastic soda bottle (empty)

dish soap

food coloring

vinegar

baking dish or other pan
15

Food Color

Vinegar

Warm

Water

Dish

Soap

Empty

Plastic

Soda

Bottle

Instructions:

1. First, make the mixture for the “cone” of the volcano. To do this, mix 6 cups of flour, 

2 cups of salt, 4 tablespoons of cooking oil, and 2 cups of water. The resulting 

mixture should be smooth and firm (more water may be added if needed).

2. Stand the soda bottle in the baking dish, and mold the dough around it into a

volcano shape. Don’t cover the hole or drop dough into it.

3. Fill the bottle most of the way full with warm water and a few drops of

red food coloring.

4. Add 6 drops of dish soap to the bottle contents. The soap helps trap the bubbles 

produced by the reaction, which creates better lava.

5. Add 2 tablespoons of baking soda to the liquid. Slowly pour about 1 cup of vinegar

into the bottle. Watch out—eruption time!

6. Clean up when you are done.

Tips:

The “lava” happens as a result of a chemical reaction between the

baking soda and vinegar. In this reaction, carbon dioxide gas is produced, 

which is also present in real volcanoes.

As the carbon dioxide gas is produced, pressure builds up inside the plastic 

bottle, until the gas bubbles (thanks to the detergent) out of the “volcano.”

The red food coloring results in red-orange lava. Add some red, yellow, and 

even purple, for a bright display!

17

Vinegar

Baking

Soda

Junior Explorer Pledge

 As a Bureau of Land Management Junior Explorer, I promise to:

• Do all I can to help preserve and protect

the natural and cultural resources of our public lands.

• Be aware of how my actions can affect other living things

and the evidence of our past.

• Keep learning about the importance of nature and our 

heritage.

• Share what I have learned with others.

 Date Explorer Signature
18

"
19

Answer Key

Activity 1: Growth Speed of Giant Trees

300 ÷ 2 = 150 years

Activity 2: A Different Time, A Different Place

Activity 4: Colorful Ash Cultivates Unique Growth

Activity 5: Undercover Work

1. slow, erosion

2. weather, water

3. streams, rivers

4. landslide

5. petrified

O N J A Y L L Q P Z W A P Y M U B S W U

R R H Z F J I H O H G B A G L C K V X K

S E N M D M A P E A H W I E Y R D L I W

H Y T W S C K A U Q M R N V F C Y W X V

L A K S E A T H X D H Z T Y C C P U R H

V G W L A G G F I S W U B A Z X V O H K

U X I K R A G E U W Z U R M U P F W C W

T A Q A S U V R B P L L U D V F A H T Z

G P S L Z B B A G R E A S E W O O D E C

Y S D W W T E M L N U Y H K O P N F V U

F X R O I P B A O S P S N L F K O H K D

J O S B S E Q M R H X J H D S Z I A L T

Z P B J K O E Z D D E E W Y Z A R C I H

L A V K G T G B U E N F S L V I R Y M E

R O Z M S N A C Y C S X Y V O A H E H L

V F P N S P Z J P D P V N A V F D I H Y

M Q E R I C E G R A S S G P R S Q I I P

W P Q D R R T K F D I G M F S N K B T O

S W T T P R G V A Z U T T N G P U Y Y D

G X J W X Z H V J W A Q A A L Y P S S Y

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Activity 7: Rock Layer Formation

Diagram 3: C, F, D, A, E, B

Diagram 4: L, A, G, F, H, K, C, D, 

M, B, J

Activity 8: Petrification Process

Across

2. silica

4. cells

7. gemstones

8. slow

9. Idaho

Down

1. ash

3. climate

4. crystals

5. petrified

6. miners

Activity 9: What Am I?

1. redwood

2. volcano

3. mineral

4. erosion

5. geology

Activity 10: A-Mazing Volcanoes
BLM/ID/GI-15/001+8367