• Overlooking Chetro Ketl

    Chaco Culture

    National Historical Park New Mexico

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.

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