Devils Tower: A Landmark Revealed by Erosion
Long before Devils Tower rose above the forests and grasslands of northeastern Wyoming, its rock was hidden underground. Today, the steep-sided formation stands roughly 1,267 feet above the nearby Belle Fourche River. Its long, parallel columns make it look like a giant bundle of stone, but the tower was not built one column at a time. Its story begins with molten rock, continues through millions of years of erosion, and still includes questions geologists cannot fully answer.
A landscape with a long history
The colorful hills around Devils Tower contain layers of sedimentary rock. These layers formed from materials such as sand, mud, and minerals deposited in ancient environments. Over immense periods, the deposits hardened into rock. Some of the reddish rock visible near the tower formed long before the tower’s magma cooled.
Magma is molten rock beneath Earth’s surface. At Devils Tower, magma pushed upward into older sedimentary rocks and cooled underground. Once it cooled and hardened, it became igneous rock, a kind of rock formed from cooled magma or lava. The tower’s igneous rock is known as phonolite porphyry. It contains visible crystals set in a finer-grained background.
- deposited:
- Left or laid down in a place.
- crystals:
- Solid mineral structures with an organized internal pattern.
- evidence:
- Information used to support an explanation or conclusion.
- precise:
- Exact or clearly defined.
- tributaries:
- Smaller streams or rivers that flow into a larger river.
- resistant:
- Able to withstand a force or process, such as erosion.
- significance:
- Importance or meaning.
- designated:
- Officially named or chosen for a particular purpose.
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Preview questions from this passageShowHide
- 1How did cooling and erosion play different roles in forming the tower visible today?
- 2What evidence shows that the tower's columns have changed since they first formed?
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About this report passage for Middle School
“Devils Tower: A Landmark Revealed by Erosion” is a report reading passage about Geology of Devils Tower, written for Middle School. It takes about 6 minutes to read (834 words) and comes with an interactive quiz and a printable worksheet with comprehension questions and an answer key.