Ann Marie Holton, age 7, of Kansas City, Kan., for her question:

HOW HIGH IS HOOVER DAM?

Hoover Dam, a popular tourist attraction located in the Black Canyon of the Colorado River 25 miles southeast of Las Vegas, is one of the highest concrete dams in the world. It is 726 feet high and 1,244 feet long.

Visitors travel from the surface and descend the equivalent of 44 stories into the dam and still do not reach its base. At the base is a great power plant.

Hoover Dam's base is 660 feet thick and it contains over 4.4 million cubic yards of concrete. This is enough to pave a two lane highway from New York City to San Francisco.

One of the world's largest bodies of water, Lake Mead, stands behind  Hoover Dam. It is about 115 miles long and in some places is about 600 feet deep.