• Overlooking Chetro Ketl

    Chaco Culture

    National Historical Park New Mexico

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  • Kin Bineola and Kin Ya' a Great Houses CLOSED

    There is no public access.

Lewis Shale

Lewis Shale
Lewis Shale
NPS Photo by Phil Varela
Petrified Tree Stump in Lewis Shale

Petrified Tree Stump in Lewis Shale

NPS Photo by Tom Lyttle

The Lewis Shale is an olive-gray marine shale thinly interbedded with claystone, siltstone and sandstone as well as scattered beds of limestone. It overlies the Cliff House Sandstone and is exposed only near the northern boundary of the park. This unit was deposited at water depths greater than the Cliff House Sandstone and represents the last significant transgression of the Western Interior Seaway into northwestern New Mexico. Few fossils have been found in the Lewis Shale unit within the park.

Did You Know?

Photo of Threatening Rock

The park considered a number of ideas for mitigating the damage that would be done if Threatening Rock fell. Proposed solutions included using dynamite to destroy it, anchoring it to the canyon wall with cables, or clearing out the rock debris behind it. It fell on January 22, 1941.