The Menefee Shale is a geological

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 stratum

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

 underlying the Chaco Wash

Chaco Wash

The Chaco Wash is an arroyo cutting through Chaco Canyon, which is located in northwestern New Mexico on the Colorado Plateau. Another arroyo known as Escavada Wash is a tributary that feeds in from the northeast, near the western end of Chaco Canyon. Chaco Wash flows northwest to become the...

, which is located in the northwestern portion of the U.S.

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 state of New Mexico

New Mexico

New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

, in what is now Chaco Culture National Historical Park

Chaco Culture National Historical Park

Chaco Culture National Historical Park is a United States National Historical Park hosting the densest and most exceptional concentration of pueblos in the American Southwest. The park is located in northwestern New Mexico, between Albuquerque and Farmington, in a remote canyon cut by the Chaco Wash...

. The Chaco Wash flowed across the upper strata of what is now the 400-foot (122 m) Chacra Mesa

Chacra Mesa

The Chacra Mesa is a high mesa massif composing the southwestern flank of Chaco Canyon, a region that is notable for its rich collection of ancient Chacoan Anasazi archaeological sites....

, gouging out a broad canyon over the course of millions of years and exposing bedrock

Bedrock

In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...

 comprising the Menefee Shale formation; this was subsequently buried under approximately 125 feet (38 m) of deposited sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

.