page_title: Sixtymile Formation
hierarchical_section_title: Sixtymile Formation
caption_attribution_description: Sixtymile Formation in Grand Canyon
context_page_description: The Sixtymile Formation is the uppermost unit of the Grand Canyon Supergroup. It is a very thin accumulation of sandstone, siltstone, and breccia that is exposed in only four places in the Chuar Valley. These exposures occur atop Nankoweap Butte and within Awatubi and Sixtymile Canyons in the eastern Grand Canyon, Arizona. The maximum preserved thickness of the Sixtymile Formation is about 60 meters. The actual depositional thickness of the Sixtymile Formation is unknown owing to erosion during the formation of the Great Unconformity and prior to deposition of the Tapeats Sandstone.
  Sixtymile Formation and the underlying Chuar Group are preserved only in a broad asymmetric fold comprising both units, called the Chuar syncline. The Chuar syncline is a doubly plunging fold, which means that along the hingeline within the axis of the syncline, beds in some areas dip toward the south, and in other areas, beds dip toward the north. The Sixtymile Formation, Chuar Group, and Chuar syncline is bounded on the east by the Butte fault zone and on all other sides by the Great Unconformity and overlying Tapeats Sandstone.
context_section_description: The Sixtymile Formation is the uppermost unit of the Grand Canyon Supergroup. It is a very thin accumulation of sandstone, siltstone, and breccia that is exposed in only four places in the Chuar Valley. These exposures occur atop Nankoweap Butte and within Awatubi and Sixtymile Canyons in the eastern Grand Canyon, Arizona. The maximum preserved thickness of the Sixtymile Formation is about 60 meters (200 ft). The actual depositional thickness of the Sixtymile Formation is unknown owing to erosion during the formation of the Great Unconformity and prior to deposition of the Tapeats Sandstone.
  Sixtymile Formation and the underlying Chuar Group are preserved only in a broad asymmetric fold comprising both units, called the Chuar syncline. The Chuar syncline is a doubly plunging fold, which means that along the hingeline within the axis of the syncline, beds in some areas (Nankoweap Canyon) dip toward the south, and in other areas (Lava Chuar Canyon), beds dip toward the north. The Sixtymile Formation, Chuar Group, and Chuar syncline is bounded on the east by the Butte fault zone and on all other sides by the Great Unconformity and overlying Tapeats Sandstone. The hingeline of the Chuar syncline parallels the trace of the Butte fault, suggesting a genetic relationship between the syncline and the fault.
  In descending order, the Sixtymile Formation is underlain by the Chuar Group, Nankoweap Formation, and the Unkar Group. The Unkar Group lies unconformably upon deeply eroded granites, gneisses, pegmatites, and schists of the Vishnu Basement Rocks. The Nankoweap and Sixtymile formations together with the Chuar and Unkar groups comprise the Grand Canyon Supergroup.
caption: Sixtymile Formation in Grand Canyon
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