The Hoover Dam, built during the Great Depression, is one of the nation’s biggest infrastructure achievements. WASHINGTON — A massive 300-foot-wide, 150-foot-tall American flag has been draped over the Hoover Dam in Nevada as part of the celebration for America’s 250th anniversary. The installation went up on Memorial Day to honor the men and women who gave their lives in service to the country, and will light up each night until July 4. The display uses more than 550 automated LED lights and is completely powered by the dam’s hydroelectricity. According to officials, the American flag weighs about 2,000 pounds…