A century ago, the government hired unemployed young men to build America's forests, trails, and parks. Photos show FDR's 'tree army.'

A century ago, the government hired unemployed young men to build America's forests, trails, and parks. Photos show FDR's 'tree army.'

Members of the Civilian Conservation Corps (CCC) at a camp in Oregon.CORBIS/Corbis via Getty ImagesThe Civilian Conservation Corps was part of Franklin Roosevelt's New Deal.Enrollees became known as the "tree army" because of how many they planted — more than 2 billion.Today's state and national parks were created or expanded because of the CCC, too.In 1933, the Ohio River spilled over, flooding Louisville, Kentucky.Franklin Roosevelt blamed soi…