Stop 32 of 109 · The Sun Dagger
c. 1050 CE · Chaco Canyon, Ancestral Puebloans
The Rock Slabs That Turn Sunlight Into a Calendar
High on a New Mexico butte, three leaning stone slabs cut sunlight into thin daggers that mark the solstices and equinoxes, though whether they were placed there on purpose is still an open question.
Near the top of Fajada Butte, which rises about 135 meters above the floor of Chaco Canyon, three sandstone slabs, each two to three meters tall, lean against a cliff facing southeast. Behind them, someone pecked two spirals into the rock: a large one of roughly nine and a half turns, and a smaller one above and to its left.
Near midday, sunlight slipping through the narrow gaps between the slabs throws thin blades of light, "daggers," across the spirals. At the summer solstice, a single dagger bisects the large spiral for about eighteen to twenty minutes. At the equinoxes, a thinner shaft falls off-center on the large spiral while a second, smaller dagger crosses the small one. At the winter solstice, two daggers frame the large spiral from either side.
The artist Anna Sofaer recorded the effect in 1977, and it drew wide attention as a rare example of a built solar marker from the ancient Southwest. How deliberate it really is, though, remains genuinely argued: some researchers think the slabs simply fell into that position naturally, and that later observers carved the spirals to match light already falling there; others think the placement was intentional from the start. By 1989, erosion from visitors' footsteps had already shifted the slabs enough to thicken the summer dagger beyond its original width, and the site has since been closed to protect it.
Chaco flourished roughly between 850 and 1150 CE, and the descendants of the people who built it, along with other Southwestern peoples, still regard the canyon as sacred ground today.