Ancient Astronomers Built These Colorado Ruins to Align Perfectly With the Moon’s 18.6-Year Cycle

Chimney Rock National Monument, Colorado

A thousand years ago, ancient Puebloans picked the perfect spot for a city: right below two massive stone spires that lined up with the moon. Chimney Rock wasn’t just their home: it was their calendar, their temple, and their link to the stars.

This is how a rock formation high up in Colorado became sacred ground.

The Ancestral Puebloan Settlement

Ancestral Puebloans lived at Chimney Rock between AD 925 and 1125. At its peak, the settlement housed approximately 2,000 people at 7,600 feet elevation.

Archaeologists identified 91 separate structures that served as living spaces across the mesa. Amazingly, ancient workers transported water and all building materials from the valley floor 1,000 feet below.

In 1125, inhabitants burned their buildings before abandoning the settlement. No one knows exactly why they left, though drought conditions affected much of the region during this period.

The Great House Pueblo

The Great House Pueblo stands at 7,620 feet, the highest visitor-accessible point in the monument. This structure contains 36 ground-floor rooms and two kivas built in the distinctive Chacoan style.

Tree-ring dating shows construction began in 1076 with major expansion in 1093. Both dates coincide exactly with lunar standstill events visible between the twin rock spires.

Only one or two families lived permanently in the Great House. The building primarily served ceremonial functions and housed visiting dignitaries from other communities.

The Great Kiva

The Great Kiva measures 44 feet in diameter, exceeding the 35-foot minimum needed for “great” designation. Religious ceremonies and community gatherings took place in this sacred space.

Distinctive features include a bench-like structure, foot drums in the floor, and a central fire pit. Fourteen stone-lined storage vaults called cists lie beneath the floor, nine still covered with wooden planks when excavated.

No sipapu, the symbolic entrance to the spirit world common in other kivas, exists here as well.

The Pit House

Built directly on bedrock rather than dug into soil, the structure functioned as an above-ground dwelling. A ventilator shaft near floor level provided fresh air for occupants and fueled cooking fires.

The northeastern held manos and metatates for grinding corn and seeds, and northwest room excavations revealed intact cooking pots containing corn, beans, and wild seed remains.

Middle room occupants worked stone and processed animal hides using specialized hammer stones and tools.

The Guardhouse

Halfway between workers’ houses and the Great House Pueblo stood the Guardhouse. This structure stretched completely across the narrow ridge, controlling access to sacred areas above.

One family lived in this strategic location, monitoring who passed toward the Great House. It was likely more of a checkpoint than a defensive fortification.

Forest Service officials eventually removed the structure after excavation made it unstable.

The Twin Spires

Chimney Rock and Companion Rock rise 315 feet above the mesa top. From the Great House, these spires frame the rising moon during the Major Lunar Standstill.

The Major Lunar Standstill

Every 18.6 years, the Major Lunar Standstill occurs when the moon reaches maximum declination at 28.72 degrees.

At Chimney Rock’s twin spires, the alignment remains visible for several days during a three-year period.

Researchers believe Chimney Rock is the only place on Earth where a natural rock formation so perfectly frames this lunar event. The next Major Lunar Standstill visible from Chimney Rock will happen in 2042-2043.

The Chacoan Connection

Archaeologists describe Chimney Rock as the “Ultimate Outlier” of the Chacoan cultural system. Chaco Canyon, located 90 miles south in present-day New Mexico, was the ceremonial and governing heart of Ancestral Puebloan civilization between 850-1150 AD.

Of the 17 clay prayer plume holders (ceremonial objects used to hold feathers during rituals) found across all Ancestral Puebloan sites, 11 came from Chimney Rock. Lab tests confirmed that feather holders found at Pueblo Bonito in Chaco Canyon were made from the same clay as those found at Chimney Rock.

Visiting Chimney Rock National Monument

Chimney Rock National Monument is located in southwestern Colorado, about 17 miles west of Pagosa Springs via Highway 160 and Highway 151. The monument sits at 7,000 feet elevation, so expect cooler temperatures than the valley below.

The monument is open May 15 through September 30, typically from 9 AM to 4:30 PM. Access is by guided tour only – you cannot explore on your own.

Book your tour in advance through the Chimney Rock Interpretive Association website or by calling (970) 883-5359. Tours fill up quickly, especially on weekends and during peak summer months.

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