The Grand Canyon.

W. Tyson Joye/National Park Service

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5 Secrets of the Grand Canyon

What one of the world’s most breathtaking landscapes reveals about our planet

For many people, summer means it’s time for a road trip! One popular destination is Grand Canyon National Park in Arizona. Every year, about 6 million visitors head there to explore one of the world’s largest canyons. It could hold water from 1.7 billion Olympic-sized swimming pools! 

The Grand Canyon has long fascinated scientists. By studying its rocks, geologists have uncovered details about Earth’s history. “There’s no place in the world like it,” says geologist Wayne Ranney. 

Here are five amazing facts about the Grand Canyon.

1. The Grand Canyon area was a sea, then a desert, then a sea again!

Scan the canyon’s walls, and you’ll notice many rock layers of different colors. The substances that make up each layer can tell scientists about the environment in which the rocks formed.

One layer from 275 million years ago is made of sandstone, a type of . That shows the region was once covered in sand dunes. Other layers are made of limestone, a sedimentary rock composed of shells from tiny sea animals. These rocks reveal that the area was under the ocean several times over millions of years.  

The oldest rocks—those at the canyon floor—are almost 2 billion years old. These dark and formed inside mountains. 

2. The canyon was once home to wild creatures!

All sorts of ancient animals lived in the Grand Canyon area, from armored sea creatures to giant dragonflies. The remains are preserved as in the canyon’s many rock layers.

But dinosaur fossils haven’t been found in the canyon. Why? Dinosaurs lived between 230 million and 66 million years ago. Rocks from that time have been eroded, or worn away by water and wind. The youngest rocks at the canyon’s rim are 270 million years old. 

The remains of animals that lived more recently have been found at the canyon, however. Those fossils were not hardened within rock layers but preserved inside caves. Scientists have found fossils of giant sloths that lived 11,000 years ago. The remains were in caves under hardened piles of sloth dung!

A fossilized skull and an illustration of an ancient sloth.

Illustration by Kate Francis (grand canyon diagram); Roman Uchytel/http://prehistoric-fauna.com (sloth); National Park Service (fossilized sloth skull)

Fossils like this skull (right) reveal that sloths the size of grizzly bears slept inside caves at the Grand Canyon 11,000 years ago.

3. The Grand Canyon took millions of years to form—and it’s still forming!

The area that is now the Grand Canyon was once at sea level. Then, about 70 million years ago, pushed the area up from the surrounding land. Scientists think that caused groundwater to flow to the sea. 

This flowing water formed rivers. The rivers slowly eroded the layers of rock, carving a deep canyon. Then, about 6 million years ago, the rivers joined to form one long river, which was named the Colorado River. 

This river stretches from the Rocky Mountains to the Pacific Ocean. It still deepens the canyon’s floor by the thickness of a sheet of paper every year.

Rafters float down the Colorado River at the bottom of the Grand Canyon.

John Lazenby/Alamy Stock Photo

Visitors can raft down the Colorado River, which flows at the bottom of the Grand Canyon.

4. Sometimes the canyon looks like it’s filled with whipped cream.

Once every few years, visitors can witness a rare sight: clouds filling the canyon up to its rim! This usually happens in winter, after heavy rain or snow, on days when there’s little wind.

When a storm passes through the area, cold, moist air can sink deep into the Grand Canyon. The cold air becomes trapped beneath a layer of warmer air. When the cold and warm air meet, moisture in the warm air condenses, or turns from gas to liquid. That causes clouds to form. 

If there’s little wind, the clouds can stay trapped in the deep canyon for a day or two!

Clouds fill the Grand Canyon.

Moment RF/Getty Images

In the aftermath of a storm, the Grand Canyon can fill with clouds.

5. The Grand Canyon is still full of mysteries.

After 150 years of studying the canyon, geologists still have many questions about it. For instance, they’re investigating how old parts of the canyon are. 

But that’s part of what makes this place special, says Ranney. “People like the unknown.”

sedimentary rock

a type of rock that forms when layers of sediment, like dirt and sand, get pressed together

igneous

a type of rock that forms when rock melts deep underground, then cools and hardens again

fossils

the remains or traces of organisms that have been hardened into rock

tectonic plates

moving slabs of rock that make up Earth’s crust, or rocky outer layer

metamorphic rocks

rocks that form when heat and pressure inside Earth change other rock types without melting them

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