A thousand years ago, a civilization flourished at Chimney Rock, where ancestral Puebloans built high above the valley fields, water, and other resources, then left after 200 years for reasons that remain unknown. Possible explanations include drought, resource depletion, collapse of a cultural belief system or social hierarchy, or, in Pueblo traditions of migration, simply that it was time to go. One prominent theory holds that Chimney Rock was part of a larger regional network of communities centered at Chaco Canyon nearly 90 miles southwest in New Mexico, an idea supported by similarities in architecture and artifacts, and the site has been called the ultimate outlier because it embodies many Chacoan design, construction, and setting ideals. Chimney Rock is also a recognized archaeoastronomy resource in North America that reflects ancestral Puebloan knowledge and use of astronomy, with evidence suggesting rituals based on celestial events such as solstices and equinoxes. An especially important event, the Northern Major Lunar Standstill, occurs every 18.6 years when the moon rises between the two pinnacles as seen from the Great House. Geology, astronomy, archaeology, and living cultures meet here, and descendants of the ancestral Puebloans return for celebrations and traditional purposes.