Atop Fajada Butte, Chacoan skywatchers commemorated the movement of the sun and the seasons. Sunlight passed between three boulder slabs onto a spiral petroglyph to mark the sun's position on the summer solstice, winter solstice, and the equinoxes. The Chacoans had sophisticated knowledge of the sun and moon, as shown there and at other sites. Sun watching continues to play an integral role in the Pueblo world, where such markers are used to plan agriculture, set the ceremonial calendar, integrate the physical and spiritual worlds, and seek balance and harmony for all people. In 1989, researchers noticed that the light pattern on the spiral had shifted because the slabs had slipped slightly, possibly as a result of human-caused erosion at the base of the rocks, and Fajada Butte is closed to all access because of its fragile nature.