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d and plant roots rubbed away at the top of the new canyon. Below, the flowing river continued to uncover more and more levels of ancient rock.

 

Some of Earth's oldest rocks can be found here. There are many levels of granite, schist, limestone and sandstone.

 

SHIRLEY GRIFFITH: Three thousand years ago, American Indians occupied the Grand Canyon. Evidence of their existence has been found in many places. Bones, hair, feathers and the remains of plants have been found in deep, dry caves high in the rock walls.

 

The Hopi, the Paiute, the Navajo and other Native American tribes have all been in the area for at least seven centuries. However, much of what we know today about the Grand Canyon was recorded by John Wesley Powell. In eighteen sixty-nine, he became the first known white American to explore much of the canyon.

 

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JUNE SIMMS: Today, the Grand Canyon is known as one of the seven wonders of the natural world. About five million people visit the canyon each year. Most visitors walk along paths, part way down into the canyon. It takes several hours to walk to the bottom. It takes twice as long to get back up to the top. Some visitors ride mules to the bottom and back.

 

SHIRLEY GRIFFITH: The National Park Service is responsible for protecting the Grand Canyon. Visitors are not supposed to leave any trash in the canyon or remove any rocks, plants or historical objects. As the Park Service tells visitors: "Take only photographs. Leave only footprints."

 

There are helicopter and airplane rides available for visitors to the Grand Canyon. Some visitors see the canyon by taking a boat trip along the Colorado River.

 

JUNE SIMMS: And there is still another way to see the Grand Canyon. A glass walkway called the Skywalk extends twenty-one meters from the edge. The Skywalk is suspended more than one thousand two hundred meters above the bottom of the canyon.

 

Visitors pay to walk along the glass walkway which is shaped like a giant horseshoe.

 

The Hualapai Indian Tribe built the Skywalk at a cost of more than forty million dollars. The tribe owns almost four hundred thousand hectares of land in the canyon. Some people consider the Skywalk an engineering wonder. Others, however, have criticized the Skywalk and plans by the tribe for future development in the area. They say it harms a national treasure and reduces the enjoyment of one of nature's greatest wonders.

 

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SHIRLEY GRIFFITH: Our program was produced by Brianna Blake, with reporting by June Soh. I'm Shirley Griffith.

 

JUNE SIMMS: And I'm  June Simms. You can find a video about the Ringling Brothers circus train on our website, 51voa.com. You can also find transcripts and MP3s of our programs, along with podcasts and activities for learning English. Join us again next week for THIS IS AMERICA in VOA Special English.

 

 

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