Why Build the Casa Grande?

line art showing potential celestrial alignments
Suggested alignment holes in the walls of the Great House


Archeologists don't know for sure. Its original purpose remains a puzzle. Here, there are still more questions than answers.

Was it an ancient astronomical observatory? Perhaps. Why do the walls line up north-south-east-west? Unknown. We can still observe the sun and moon line up with certain holes in the wall before you, year in and year out. Were sacred ceremonies held here? Did a leader who oversaw the all-important irrigation canals work inside these rooms? Did an influential family or clan call the Casa Grande their home?

The answers remain unknown. The Casa Grande likely served many purposes, many functions. Why do you think the Ancestral Sonoran Desert People built this impressive multi-story building?

Farming societies in many parts of the ancient world worked out ways to track the seasons. The Casa Grande also has features that can be used to accurately mark the time of year.

Summer Solstice

Sunlight lines up through this small hole at sunset on the longest day of the year.

Spring and Fall Equinoxes

The rising sun lines up with twin openings in the top floor of the Casa Grande each March and September.

A Very Rare Lunar Event

The sun 'stands still' in the sky twice every year— at 'solstices.' The moon 'stands still' in the sky only once every 18.6 years. This hole marks that lunar event.

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PDF of the wayside (5,973 KB) is available.


Last updated: April 6, 2020

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Coolidge, AZ 85128


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