page_title: Chaco Culture National Historical Park
section_title: Geology
hierarchical_section_title: Chaco Culture National Historical Park / Geology
caption_attribution_description: An image of Fajada Butte, Chaco Canyon (New Mexico, United States).
context_page_description: Chaco Culture National Historical Park is a United States National Historical Park in the American Southwest hosting a concentration of pueblos. The park is located in northwestern New Mexico, between Albuquerque and Farmington, in a remote canyon cut by the Chaco Wash. Containing the most sweeping collection of ancient ruins north of Mexico, the park preserves one of the most important pre-Columbian cultural and historical areas in the United States.
  Between AD 900 and 1150, Chaco Canyon was a major center of culture for the Ancestral Puebloans. Chacoans quarried sandstone blocks and hauled timber from great distances, assembling fifteen major complexes that remained the largest buildings ever built in North America until the 19th century. Evidence of archaeoastronomy at Chaco has been proposed, with the "Sun Dagger" petroglyph at Fajada Butte a popular example. Many Chacoan buildings may have been aligned to capture the solar and lunar cycles, requiring generations of astronomical observations and centuries of skillfully coordinated construction.
context_section_description: After the Pangaean supercontinent sundered during the Cretaceous period, the region became part of a shifting transition zone between a shallow inland sea—the Western Interior Seaway—and a band of plains and low hills to the west. A sandy and swampy coastline oscillated east and west, alternately submerging and uncovering the area atop the present Colorado Plateau that Chaco Canyon now occupies.
  The Chaco Wash flowed across the upper strata of what is now the 400-foot (120 m) Chacra Mesa, cutting into it and gouging out a broad canyon over the course of millions of years. The mesa comprises sandstone and shale formations dating from the Late Cretaceous, which are of the Mesa Verde formation. The canyon bottomlands were further eroded, exposing Menefee Shale bedrock; this was subsequently buried under roughly 125 feet (38 m) of sediment. The canyon and mesa lie within the "Chaco Core"—which is distinct from the wider Chaco Plateau, a flat region of grassland with infrequent stands of timber. As the Continental Divide is only 15.5 miles (25 km) east of the canyon, geological characteristics and different patterns of drainage differentiate these two regions both from each other and from the nearby Chaco Slope, the Gobernador Slope, and the Chuska Valley.
caption: Summer thunderstorms over Fajada Butte and the Fajada Gap, near the southwestern rim of Chaco Canyon
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