Geology

Natural Features & Ecosystems

To many, the most outstanding natural features of Colorado National Monument are the park's geologic formations. In each of the canyons, visitors can see the remarkable effects of millions of years of erosion on a landscape of sedimentary rock. Two unusual natural features are common in Colorado National Monument and intrigue both scientists and visitors: biological soil crusts and potholes.

Biological soil crusts are a living groundcover that forms the foundation of high desert plant life. Potholes are naturally occurring basins in sandstone that collect rainwater and wind-blown sediment. These potholes harbor organisms that are able to survive long periods of dehydration, and also serve as a breeding ground for many high desert amphibians and insects. Both of these communities are very vulnerable to human impacts.

Geologic Activity

GEOLOGY IN ACTION! The Rock Fall of ’00 What happened? At about 9:45 in the morning on January 8, 2000, a section of cliff suddenly dropped onto Rim Rock Drive near the Liberty Cap trailhead, completely blocking the roadway. There were no injuries, but because the area was considered unstable, it was cordoned off to the public. Rim Rock Drive remained closed until the rock debris was cleared off and the road repaired.

What fell? The rocks that fell are sandstones that were originally deposited about 140 million years ago by ancient streams. Geologists describe the rocks as being from the Salt Wash Member of the Morrison Formation.

Why did they fall? The salt wash sandstone has a distinct layer of soft shale in the middle and a layer of easily eroded shales and sandstones below. Ancient earth movements have created two distinct sets of nearly vertical fractures in the salt wash sandstone. These two fracture planes meet at nearly right angles, creating large rectangular blocks that are not firmly connected to the rest of the cliff. This lack of a firm connection to adjacent rocks, coupled with the layers of weak shale, means salt wash sandstone is easily eroded in this area of the monument.

Has this happened before? Certainly. Our earth is a dynamic and ever-changing place. The rock fall of January 8, 2000 is simply a continuation of the erosion that has carved the canyons of Colorado National Monument. Erosion is a natural process, and in fact is the architect of the spectacular landscape. Examples of erosion abound within the monument in the form of already-fallen boulders, small rock falls, and stream scouring and widening during flash floods. While larger rock falls occur frequently in geologic time, it is a rare and exciting opportunity to see and study one during our lifetime. Some of these broken rocks last saw the light of day 140 million years ago when they were laid down in a streambed during the time of the dinosaurs. As geologists study them today they may reveal more about those ancient times, or they might help us understand how we may in the future predict the likelihood of future rock falls.

Geologists, engineers, and historians examined the rock fall and attempted to determine several things: - was there any immediate danger of further rock falls? - was it safe to work in the area with heavy equipment? - how much damage was done to Rim Rock Drive? - how to proceed with the clean up and repair minimizing the effect on Rim Rock Drive, which is a listed structure on the National Register of Historic Places? Considering all of these factors, Rim Rock Drive was cleared and repaired as quickly as possible.

Environmental Factors

Colorado National Monument was established to preserve, study, and enjoy the geological resources and processes as well as the canyon, mesa, and plateau ecosystems that are representative of the greater Colorado Plateau. These ecosystems are affected by many factors, both within and outside monument borders. Over time, ecosystems have been altered by geological processes such as flash floods and rock falls, by the occupation, development, and use of surrounding lands and by management practices within monument boundaries, such as building and utility construction, fire prevention activities, and bison introduction. Increased upstream use of water has an impact on rare and sensitive riparian areas. Habitat loss and fragmentation have resulted in species loss, the white tailed prairie dog being the most recent example. Invasive plants can threaten the survival of native species.

Local population, which has doubled since 1970, brings forth some issues as well. Residential areas directly adjoin the monument boundary both in the Grand Valley and, at a lesser density in and near Glade Park. Dense residential development on private land bordering the park has sharpened the edge of the monument, cutting across the grain of natural processes such as flash floods and wildlife movements. Rapid urban development also increases the demand for recreation. Unfortunately, this also brings impacts such as damage to biological soil crusts, noise intrusion, law enforcement incidents, vandalism, destruction, and theft of archeological and paleontological resources, and increased traffic. Bicycles, touring automobiles, and commuters struggle to share a winding, historic road. The challenge to National Park Service management, visitors, and the community is to prevent further loss of the monument's unique environment and ecosystems and, where feasible, to restore species and ecosystems, thus preserving a quality experience for all who visit, now and in the future.

Soils

The desert climate allows only sparse growth of desert shrubs and grasses, thus the importance of fragile biological soil crusts (formerly known as cryptobiotic soils) to provide soil stability as well as a nitrogen source for other plants/organisms to utilize. Soils in the monument are highly permeable allowing moisture to be channeled and trapped between rock layers and along fissures contributing to lower elevation springs and seeps.

Geologic Formations

The Colorado National Monument is located within the Canyon Lands Basin of the Colorado Plateau physiographic province (SCS 1978). Landscapes are characterized by exposures of colorful, gently dipping sediments that have been differentially eroded to form high plateaus, bold escarpments, and deep canyons. Sandstone monoliths and steep walled canyons sculpted from years of natural erosion provide scenic, educational, and scientific benefits to visitors.