Geology

Hovenweep is defined by its geology, from the sandstone-block structures to the boulder-dotted canyons to Sleeping Ute mountain range looming in the east.

NPS photo/Austin Tumas

 

A sea of rippling rock, cut by canyons and marked by mountains, this landscape is a testament to the powers of wind, water, and time. Isolated mountain ranges called laccoliths dot the horizon in all directions. Potholes catch rainwater for living things big and small. Biological soil crusts let plants thrive. From the first Paleoindian hunter to modern farmers, all lives here are shaped by the rock.

 

The Tilted Table

Hovenweep is part of a region called the Colorado Plateau, a high desert covering the Four Corners area of the Southwest. Ninety percent of the Colorado Plateau is the San Juan River Basin, or land where water drains to the San Juan River. This drainage carved the winding canyons in Hovenweep, giving shelter and water to plants and wildlife, and later people.

Within the basin and plateau, Hovenweep is located on Cajon Mesa. Mesa means "table" in Spanish and refers to a wide, raised landform with a flat top. The flat top of Cajon Mesa is tilted slightly to the southwest. Elevations near Cutthroat Castle reach 6,800 feet but fall to 4,900 feet near the Cajon unit. This elevation change means Cutthroat Castle has higher rainfall and more trees than Cajon.

 

The Burro Canyon Formation conglomerate is the lasting clue of an ancient river that deposited mud and rocks over 100 million years ago. This conglomerate is visible on the Square Tower loop trail as it heads into the canyon.

NPS photo

A Tale of Two Layers

At Hovenweep, the top rock layer is Dakota Sandstone. Dakota Sandstone is made up of yellow/gray sandstone, mudstones, and a few thin beds of coal. This layer represents transitions from river to swamp to marine conditions and was deposited 30-70 million years ago in the late Cretaceous period. Ancestral Puebloans used the sandstone to make manos and metates, tools used to grind corn. This is also the layer where they gathered the masonry blocks to build Hovenweep's famous towers and structures.

Look for Dakota Sandstone at Hovenweep:

• open slickrock on canyon rims
• coal deposits along the trail to Twin Towers and in the canyon crossing (Square Tower Loop)

Below the Dakota Sandstone is Burro Canyon Formation, the only other rock layer, or stratum, visible in Hovenweep. Burro Canyon Formation is made of white conglomerate, green shale, mudrock, and sandstone layers with interspersed pebbles and cobbles of chert as well as limestone and quartzite. This layer was deposited by an ancient river and floodplain over 100 million years ago in the early Cretaceous period. Ancestral Puebloans used rocks from Burro Canyon Formation to make tools like chert knives and arrowheads.

Look for Burro Canyon Formation at Hovenweep:

• along the canyon crossing section of the Square Tower Loop trail
• along the trail near Cutthroat Castle

 

Potholes in the sandstone collect rainwater. They provided a valuable source of water for all who lived here, including the ancestral Puebloans.

NPS photo

Where’s the Water?

Hovenweep’s two rock strata are perhaps the most significant features of the park. These two layers act as a sponge and funnel for water, an essential resource for life in the desert.

When rain falls, some water collects on the ground in potholes. The rest soaks into the porous Dakota Sandstone. Eventually, the water hits the Burro Canyon Formation, which is much denser than the Dakota. The water cannot travel down throught the Burro Canyon Formation, so it flows horizontally instead. When the water reaches a cliff edge, it seeps out of the rock and forms a freshwater spring.

Springs were essential to Hovenweep's earliest people, who hunted and gathered here. Springs were also essential to the ancestral Puebloans who may have prayed for rain here in the 1200s. Tribal consultants from some descendant communities explain that water can be a channel to carry prayers. The springs at Hovenweep are part of a watershed that connects all the way to the Sea of Cortez, so they could serve as an access point for prayers to reach this essential source of moisture. Today, springs remain sacred to many Native communities. The springs at Hovenweep connect descendants to their ancestors who built these towers.

 

Red Dirt, Green Thumb

The red-brown loess soils at Hovenweep today were blown here by southwestern winds less than 10,000 years ago. This soil contributed to a major lifestyle change for the ancestral Puebloans, from hunting and gathering to agriculture. Composed of fine-grained sandstone and iron oxide, this soil supported crops of corn, beans, and squash for hundreds of years. Native consultants suggest this agricultural lifestyle is the reason Hovenweep was built as a place for ceremony to call the rain. Today, the same rich loess soil supports alfalfa, beans, wheat, and safflower for farmers in nearby Montezuma Valley communities.