Geology of Capitol Reef National Park
Nestled between Canyonlands National Park and Grand Staircase-Escalante National Monument in south-central Utah, Capitol Reef National Park hosts a variety of flora and fauna and a wealth of geologic history. The park lies on some 377 square miles and showcases the Waterpocket Fold, a dramatic wrinkle in the Earth that extends over 100 miles.
Capitol Reef National Park lies within the Colorado Plateau Physiographic Province, which is situated between the Rocky Mountains and the Basin and Range region. The Colorado Plateau hosts nine national parks and several national monuments. Although the highlight of Capitol Reef’s geology is its Waterpocket Fold, there is much more to its geologic history.
Capitol Reef’s geology can be traced back over 250 million years to the Permian period. At that time, the park was covered by dunes with a climate and conditions most similar to those of the Saharan Desert today. These conditions are captured by the White Rim Sandstone as the lowest level on the stratigraphic column. By 225 million years ago, the landscape transitioned to a much wetter climate with tropical forests, ferns, and swamps. By 180 million years ago, the climate dried again and was once again covered by vast dune fields for millions of years, visible today in the large crossbeds of the Navajo Sandstone. The desert climate became a wetter, coastal area about 140 million years ago in the area that is now recorded by depositional layers of sandstone and shale.
All of these landscape and climatic changes are illustrated by the stratigraphic column, layers of rock, visible at the park. Different types of rocks, their thickness, compactness, variety, and orientation give geologists a window into the past. The stratigraphic column at Capitol Reef illustrates the dramatic changes that area has undergone in the past 200 million or more years.
Millions of years after most of the sedimentary layers were deposited, the Colorado Plateau experienced uplift due to the large-scale tectonic forces of the Laramide Orogeny, a mountain-building event that occurred 35 to 75 million years ago. Across the region, rock layers were thrust up thousands of vertical feet, while remaining roughly horizontal. The Waterpocket Fold at Capitol Reef is an exception to this regional trend. Here, the sedimentary rocks that above the fault were more ductile and merely folded instead of faulting, creating the large monocline. Rock layers on the western side of the fold are lifted about 7,000 feet higher than those to west.
The monocline would not have been visible at Earth’s surface until the more recent uplift of the Colorado Plateau in last 20 million years. The Colorado Plateau has been uplifted approximately 12,000 feet since the end of the Cretaceous period. This uplift also accelerated erosion exposing the Waterpocket Fold. The forces of erosion created the structures for which Capitol Reef is in part named and continue to sculpt the dramatic landscapes in the desert southwest. Where the rock around the Navajo Sandstone has been worn away it has created dome-like structures in the park. Early settlers of the region thought these domes resembled the Capitol building in Washington, D.C. These same settlers referred to the Waterpocket Fold as a reef because it posed a physical barrier to transportation much like a reef at sea.
Despite its desert climate, water is still the driving force of erosion in the Park. Summer monsoons can rapidly fill both the perennial and ephemeral streams in the Park causing flash flooding. These streams can carry large amounts of sediment that scour the landscape as they flow rapidly downstream. Water influences slower erosional processes as well. Water moves through porous rock such as sandstone and dissolves water-soluble calcium carbonate as it flows over time. This type of chemical weathering creates tafoni, a lacy, porous structures with tiny divots and arches.
Water can flow very fast during flash floods and can transport large amounts of sediment, including large boulders, as it travels. These sediments and rock fragments gouge the rocky surface below and the strong erosive power creates depressions in the rock below. When the water evaporates from the stream, some water may be left in these depressions, known as waterpockets, which help to store water and sustain life in the arid climate.
Another interesting feature of Capitol Reef National Park are the random black boulders found scattered around the park which stand out against the background of lighter-colored sedimentary rocks. These boulders originated from 20- to 25-million-year-old lava flows in the surrounding mountains. During glacial periods within the past 150,000 years, glaciers eroded volcanic rocks within the nearby mountains and transported them downslope into Capitol Reef National Park.
A number of other geologic features can be found in the park, including: classic elongated “strike” valleys, dikes and sills (volcanic deposits), intrusive gypsum domes, landslide deposits, fossilized oyster reefs, petrified logs, dinosaur bones, and colorful, rolling bentonitic hills.
