Devils Tower is a 1,270 foot tall igneous rock formation located in northeastern Wyoming that was formed approximately 50 million years ago. It is composed of columns created by cooling magma. Over the past 1-2 million years, erosion has exposed the resistant igneous rock after wearing away overlying sedimentary layers. Devils Tower was the first national monument designated in the United States in 1906 and is an important cultural site for several Native American tribes.

1. Devils Tower
By: Elizabeth Bender
GEO 111 Fall 2012

2. Devils Tower
Warning: Notice is hereby given that
any person or persons who injure or
destroy or, without specific authority
from the Secretary of the Interior,
excavate or appropriate any historic or
prehistoric ruin, monument, object of
antiquity, or of scientific interest, for the
protection of which this reservation was
created, will be subject to arrest and
punishment under the provisions of the
acts of Congress approved February 6,
1905, and Jun 8,1908.

3. The Basics
Approximately 300 miles north of Cheyenne,
Wyoming, lies American's first National
Monument.

4. The Basics
It stands 1,270
feet above the
Belle Fourche
River below,
and measures
180 feet east to
west and 300
feet north to
south.

5. The neighborhood
There are three named layers of sedimentary rocks
exposed at the base of Devils Tower.

6. The neighborhood
The oldest layer at the bottom
is called the Spearfish
Formation, named after the
town Spearfish, South
Dakota. This layer was
formed during the Triassic
Epoch approximately 240
million years ago, when
most of the surrounding
area was part of the sea.
The composition of the
Spearfish Formation
includes mudstones and
sandstones.

7. The neighborhood
The middle layer is
known as the
Gypsum Springs
Formation and is
mostly gypsum.
It was formed
during the
Jurassic Epoch
150 million years
ago. Gypsum is
formed in natural
saline waters.

8. The neighborhood
The final layer of Devils
Tower is the Sundance
Formation. This is the
youngest formation of
the monolith, forming
relatively shortly after
the Gypsum Springs
Formation. The layer is
named after the
Sundance Sea in which
it was deposited and
ripple marks from
receding water can still
be seen within this
layer.

9. Formation
Devil's Tower is an igneous rock formation
created by intrusion. Igneous intrusion
occurs when magma solidifies before it
breaks through Earth's crust. The layer
above the intrusion is pushed skyward
creating, in this case, a massive bulge under
the sedimentary rock crust.
As the magma cooled, it shrank it size, forming
the four, five, six, even seven sided pillars of
Devils Tower.
As the continents shifted and water eroded away
the sedimentary layers, the phonolitic
porphyry monolithic pluton was exposed.
Geologist believe that while Devils Tower formed
from cooling magma 50 million years ago
during the Eocene Epoch, but it was not
exposed until 1-2 million years ago.

10. Additional Research Needed
Other theories state that Devils Tower is a laccolith or
a volcanic neck. Geologists argue that Devils
Tower would be much larger than it is if it were a
laccolith, and there is no evidence of volcanic
activities in the last 50 million years in the area.
Click to
watch

11. Weathering & Erosion 101
The 1,000 feet of sedimentary layers have eroded over the last
1-2 million years exposing the much harder igneous rock
below. Some layers washed away with the receding
Sundance Sea. Water of the Belle Fourche River Valley have
washed away the loose soil and the eroded debris from the
damaging rain and snow. Erosion exposed the monolith as it
stands today. Frost wedging continues to break off small
pieces that are swept away by water, wind, or people.

12. Erosion of Arid Land
Wyoming, though once a body
of water, is now a relatively
arid land. The base of Devils
Tower shows evidence of
differential weathering and
erosion. The sedimentary
layers remaining at the base
have eroded much faster than
the igneous rock tower above.
This has created the different
slope and the dramatic
distinction between the two
types.
The obviousness of the impressive change between the igneous and sedimentary
layers is due to the arid climate of Wyoming.

13. Erosion of Arid Land
The wind has also affected areas
of Devils Tower. The monolith
and surrounding areas are
subject to deflation and
abrasion. Dry particles are
blown away, in deflation, and
deposited miles away. Sands
that are swept away don't
leave without abrading the
solid surfaces. These Aeolian
processes are not as
destructive as water, but signs
Click to
are prevalent at Devils Tower
watch
and evidence can be found in
the surrounding areas of
Aeolian deposited particles.

14. Very Brief Human Geography
Before it was named a
national monument,
Devils Tower was
believed to be formed by
the claws of a giant bear
as it was chasing two
girls of the native Crow
Tribe. A spirit made the
rock grow until the bear
could no longer reach
them.
1906 FDR made Devils
Tower America’s first
national monument.

15. Very Brief Human Geography
In 1977, Steven
Spielberg directed
“Close Encounters
of the Third Kind,” a
movie about UFOs
and supernatural
activities
surrounding the
monolith.