Chimney Rock National Monument

National Monument, Proclaimed 2012, On San Juan National Forest Land. The Highest And Most Remote Of The Chacoan Outliers, And The Only One Built Where The Northern Lunar Standstill Moon Rises Precisely Between Two Rock Spires Once Every 18.6 Years. · Pagosa Springs, Colorado

Chimney Rock is the reason people argue that Chacoan architecture was astronomical before it was anything else. Two rock spires stand on a high mesa above the Piedra valley, and a hundred miles north-east of Chaco Canyon somebody built a great house directly behind them - twice, in AD 1076 and 1093, dates known precisely because the roof beams survived and tree rings can be counted. Both years were northern lunar standstills, the moment in an 18.6-year cycle when the moon rises at its furthest north, and at that moment, from the great house and from nowhere else, the moon comes up exactly between the two spires. The masonry is Chacoan, brought from a culture centred far to the south-west, on the highest and most remote outlier known. It is seasonal, reached by a steep road, and the great house can only be visited with a guide - which means the alignment that explains the whole site is something you have to be taken to, on a mesa that is closed for half the year.

3179 Highway 151, Pagosa Springs, Colorado, 81147, United States

SEASONAL - the monument is generally open from mid-May to the end of September and is CLOSED THROUGH WINTER, with the access road unmaintained when shut. THE GREAT HOUSE PUEBLO CAN ONLY BE REACHED ON A GUIDED TOUR; the lower trails and the visitor cabin are self-guided within opening hours. Special programmes are run for the full moon and for the solstices, and the lunar standstill events - the reason the site exists - occur only around every eighteen and a half years. The access road climbs steeply and is unsuitable for large vehicles.

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