The western flank of the Hoover Dam holds a celestial map that marks the time of the dam’s creation based on the 25,772-year axial precession of the earth.
by Alexander Rose
Jan 29, 02019
One of the two massive bronze cast sculptures that flank Hoover Dam’s Monument Plaza. (Photo by Alexander Rose)
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.
Marking in the terrazzo floor of Monument Plaza showing the location of Vega, which will be our North Star in roughly 12,000 years. (Photo by Alexander Rose)
I was particularly interested in this monument because this axial precession is also the slowest cycle that we track in Long Now’s 10,000 Year Clock. Strangely, little to no documentation of this installation seemed to be available, except for a few vacation pictures on Flickr. So the last time I was in Las Vegas, I made a special trip out to Hoover Dam to see if I could learn more about this obscure 26,000-year monument.
I parked my rental car on the Nevada side of the dam on a day pushing 100 degrees. I quickly found Monument Plaza just opposite the visitor center where tours of the dam are offered. While the plaza is easy to find, it stands apart from all the main tours and stories about the dam. With the exception of the writing in the plaza floor itself, the only information I could find came from a speaker running on loop, broadcasting a basic description of the monument while visitors walked around the area. When I asked my tour guide about it, he suggested that there may be some historical documentation and directed me to Emme Woodward, the dam’s historian.
Left: Monument Plaza with access road on left. (Image courtesy of US Bureau of Reclamation). Right: Hansen laying out the axial precession. (Image courtesy of US Bureau of Reclamation)
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