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.
-- the surface area of Lake Mead is 146,000 acres ... -- has a power generating capacity of 2.08 million kilowatts ... -- cost ONLY $49,000,000 to build the Hoover Dam ... -- cost $165,000,000 to complete the Boulder Canyon Project that includes the Imperial Dam, Hoover Dam and the American Canal ...