Chaco great houses feature precise astronomical alignments; civilization collapsed after 50-year drought. Anna Sofaer's Solstice Project identified astronomical alignments at all of Chaco's great houses In 1977, Sofaer discovered the Sun Dagger on Fajada Butte, where light passes between three sandstone slabs to illuminate a spiral petroglyph during solstices, equinoxes, and key lunar stations Some great houses align to the sun, others to the 18.6-year lunar major and minor standstills

Anna Sofaer's Solstice Project found all Chaco great houses align to astronomical events, including the 1977 Sun Dagger on Fajada Butte. Roads from the canyon ended at natural features, not settlements. A 50-year drought post-1130 CE ended great house construction, sending Ancestral Pueblo north to Mesa Verde.

Key Facts

  • Anna Sofaer's Solstice Project identified astronomical alignments at all of Chaco's great houses
  • In 1977, Sofaer discovered the Sun Dagger on Fajada Butte, where light passes between three sandstone slabs to illuminate a spiral petroglyph during solstices, equinoxes, and key lunar stations
  • Some great houses align to the sun, others to the 18.6-year lunar major and minor standstills
  • Over 200 great houses were built across the broader Chaco region
  • A road system radiated from Pueblo Bonito Great House but terminated at natural features like canyon edges, the Vesa mountains, and small bodies of water
  • The roads show little compaction, suggesting they were not used for regular trade or transport
  • Around 1130 CE, a 50-year drought struck the American Southwest
  • Chaco habitation continued in diminished form until about 1200 CE, but no new great houses were built
  • A brief population surge occurred at Aztec Ruins before it too was abandoned
  • Ancestral Pueblo migrated north to Mesa Verde and Hovenweep in southwestern Colorado, chosen for their reliable deep springs

Related site: Pueblo Bonito Great House — view location, images, and history on the Ancient Nerds map.

Source: How was Chaco Canyon really built? by Archaeologist Ed Barnhart