Save. Jupiterimages/Photos.com/Getty Images. It's easy to mistake lichens as the cause of tree or branch death because they tend to grow on sick trees. In fact, the reason they turn up is because a sick tree has a thin canopy and lets in the sun that makes lichens grow.ave. Jupiterimages/Photos.com/Getty Images. It's easy to mistake lichens as the cause of tree or branch death because they tend to grow on sick trees. In fact, the reason they turn up is because a sick tree has a thin canopy and lets in the sun that makes lichens grow.
4 Hoover Dam. Hoover Dam is one of the world's great engineering marvels. This massive structure, completed in 1935, crosses the Colorado River, linking Arizona and Nevada. It is 726 feet high and 1,244 feet long. Lake Mead, held back by the Hoover Dam, is the largest artificial lake in the United States. It is 110 miles long, and holds the equivalent of two years of flow of the Colorado River.
3. Hoover Dam created Americaâs largest reservoir. Formed by the damning of the Colorado River, Lake Mead, the nationâs largest reservoir, covers about 248 square miles and is capable of holding some 28.9 million acre-feet of water (an acre-foot is equivalent to about 325,000 gallons).