​Colorado river's Hoover Dam contains enough concrete to pave a standard highway from San Francisco to New York City, and the 90-year-old engineering marvel is still growing stronger

Standing in the brutal heat of the black canyon, Hoover Dam on the great Colorado river, was not just a construction project, it was a landmark example that redefined engineering. One of the most stunning aspects of this massive concrete structure is that it has never actually finished its physical transformation.

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