Hoover Dam<span>, once known as Boulder Dam, is a concrete arch-gravity dam </span>in<span> the Black Canyon ....</span>Construction<span> of a rail line joining Las Vegas and the dam site began </span>in<span> September </span>1930<span>. .... Falling objects were the most common cause of death on the dam site; the highscalers' work thus </span>helped<span>ensure</span><span> worker safety</span>
