On the western flank of the Hoover Dam stands a little-understood monument, commissioned by the US Bureau of Reclamation when construction of the dam began in 01931. The most noticeable parts of this corner of the dam, now known as Monument Plaza, are the massive winged bronze sculptures and central flagpole which are often photographed by visitors. The most amazing feature of this plaza, however, is under their feet as they take those pictures.

The plaza’s terrazzo floor is actually a celestial map that marks the time of the dam’s creation based on the 25,772-year axial precession of the earth.

source: jwz