1 . A giant dam was built many years ago to control the Colorado River in the U.S. This dam was built to protect the land and houses around the river.

This huge dam is in the Black Canyon. It is possible to drive a car from one side of the river to the other on a road, which is on the top of the dam. This dam is so big that there is an elevator inside. The elevator goes down forty-four stories from the road to the bottom. There is enough concrete in this dam to build a highway from New York to San Francisco. Thousands of people worked on this dam for five years.

This huge dam was called Boulder Dam when it was finished in 1936.Later it was renamed Hoover Dam in honor of a president of the United States. Hoover Dam, one of the highest dams in the world, is situated between the states of Arizona and Nevada.