The Geology of Yucca House National Monument, Colorado

Yucca House National Monument lies on the gently sloping eastern flank of Sleeping Ute Mountain, at the edge of the Montezuma Valley west of the Mesa Verde escarpment, in Montezuma County, southwestern Colorado. Authorized on December 19, 1919, the 34-acre monument protects an unexcavated thirteenth-century Ancestral Pueblo community center, valuable for research and interpretation.

The pueblo

Yucca House is a “valley pueblo”: a multi-story masonry pueblo with a well-preserved Great House, several towers set in small plazas, a bi-wall structure, many kivas, and a ceremonial plaza with a great kiva, partly enclosed by an imposing wall on the north. Its mix of architectural styles suggests that different groups lived there at the same time. It was occupied first from about 1050 to 1150 CE and again from about 1225 to 1300 CE.

Built from an ancient sea

The bedrock beneath the monument is mostly the Upper Cretaceous Juana Lopez Member of the Mancos Shale, laid down in the Western Interior Seaway when it flooded the Four Corners region. It holds well-preserved marine fossils — ammonites, bivalves and oysters — and is made of soft limy shale and hard limestone layers. The southern tip of the monument sits on the similar Montezuma Valley Member of the Mancos Shale.

The ancient builders quarried the fossil-rich limestone of the Juana Lopez Member for their walls, and Cretaceous fossils can still be seen in the building blocks visible in the rubble mounds — fossils within an archeological site. Loose sediments on the nearby mountains let rainfall soak in and feed the historic Aztec Spring, which helped draw settlement here.

Masonry ruins at Yucca House. Image from the National Park Service’s page.

All fossils in national parks are protected under the Paleontological Resources Preservation Act of 2009.

Soils and region

The Park Service’s Soil Resources Inventory for the monument maps six soil units with eight soil types; healthy soils are key to the plants, animals and landscape the park protects. Yucca House belongs to the Colorado Plateaus province and shares its geologic history with the wider region.

Sources

Based on "NPS Geodiversity Atlas—Yucca House National Monument, Colorado," Geologic Resources Division, National Park Service; a work of the United States government in the public domain.