Geodiversity refers to the full variety of natural geologic (rocks, minerals, sediments, fossils, landforms, and physical processes) and soil resources and processes that occur in the park. A product of the Geologic Resources Inventory, the NPS Geodiversity Atlas delivers information in support of education, Geoconservation, and integrated management of living (biotic) and non-living (abiotic) components of the ecosystem.
Geologic Features and Processes
The park’s namesake, is the dominant feature of the landscape. In contrast to most of the canyons in the western United States, the Black Canyon is in many places deeper than it is wide. The average depth of the canyon is 610 m (2,000 ft), with a maximum width of 823m (2,700 ft), just north of Warner Point to a minimum of 533 m (1,750 ft) at The Narrows. The Gunnison River has an usually steep gradient over the length of the gorge. It falls about 655 m (2,150 ft) from the canyon head at Sapinero to the mouth at the junction with North Fork, a distance of just 80 km (50 miles). This is an average drop of 13 m (43 ft) per mile (Hansen, 1965). For comparison, the Colorado River in the Grand Canyon only descends an average of 2.3 m (7.5 ft) per mile.
Many geologic processes acted in concert to create the precipitous depths of the Black Canyon. The most obvious processes evident today include the turbidity of the river carrying mud and debris, occasional rockfalls from high cliffs, and the relentless movement of landslides into the depths. Other more subtle processes such as gullying, frost action, and chemical weathering (acid rain) increase the material available for the river to wash away.
The process of erosion is responsible for the excavation of the canyon. However, the coincidental interplay of several other geologic factors was necessary to remove more than 25 cubic miles of rock from the landscape along such a narrow course through incredibly hard metamorphic rocks. Prior to the Gunnison Uplift, the Gunnison River followed a course through relatively soft Mesozoic and Cenozoic volcanic and sedimentary rocks. The present path of the river is controlled by this previous course; it has been impressed on the hard, underlying Precambrian rocks due to relatively rapid Gunnison Uplift event.
Some of the geoheritage features of the park include:
- Black Canyon of the Gunnison is one of the one of the best exposures of ancient (nearly 2 billion years old) Precambrian-aged rocks in the world.
- The canyon showcases spectacular, dark colored volcanic and metamorphic rocks that have been deeply incised by the Gunnison River.
- Pink colored pegmatite dikes with crystals up to 6 feet in length criss-cross the canyon walls.
- The 53 mile long canyon is one of the narrowest (1,100 feet) and deepest in the western U.S. (greater than 2,700 feet). The river gradient (96 feet per mile) is the 5th steepest mountain descent in the world.
- The Gunnison River gorge contains one of the most spectacularly exposed faults in Colorado—the Ute Indian fault which formed during the Laramide Orogeny, a period of great mountain-building in Colorado.
Paleontological resources are documented in the park and consist of Jurassic and Cretaceous fossil plants, invertebrates, vertebrates (fragmentary) and trace fossils. The fossil rich Morrison Formation is exposed within Black Canyon - Curecanti and dinosaur fossils continue to be found locally in this formation. Other units, such as the Mancos Shale and the Dakota Sandstone, also contain fossils that should be catalogued.
All NPS fossil resources are protected under the Paleontological Resources Preservation Act of 2009 (Public Law 111-11, Title VI, Subtitle D; 16 U.S.C. §§ 470aaa - 470aaa-11).
Through incredible erosion, the Gunnison River has exposed a wide range of rock types, from 1.7 billion year old gneiss and schist to Mesozoic – Cenozoic fossiliferous sedimentary rocks and modern unconsolidated sediments.
The steep, “black” walls of Black Canyon are composed of Precambrian granites, gneisses, gabbros, diorites, pegmatites, and schists. The canyon itself is considered one of the best exposures of these ancient rocks in the world.
Directly atop the Precambrian rocks, lie Mesozoic and Cenozoic sedimentary strata. No Paleozoic sedimentary rocks exist in the Black Canyon – Curecanti area. The absence of Paleozoic strata creates an unconformity, indicating that approximately 370 million years of earth history are missing from this landscape. The Entrada Sandstone, Wanakah Formation, and Morrison Formation represent Jurassic time in the area. The fossils and depositional structures within these rocks record a vast array of Jurassic climates and environments.
Above the Jurassic rocks are the Cretaceous sandstones, shales, and coal beds of the Dakota Sandstone and Burro Canyon Formation. The muds of the Mancos Shale, the volcanic breccia of the Cimarron Ridge Formation, and the brown shales and calcareous sandstones of the Fruitland Formation and Pictured Cliffs Sandstone complete the Cretaceous strata at Black Canyon – Curecanti.
At the end of the Laramide orogeny volcanic activity erupted across the area resulting in large deposits of volcanic ash, tuff, and breccia. These and other Tertiary igneous rocks cap the regions mesas today. Specific formations include West Elk Breccia, Blue Mesa Tuff, Dillon Mesa Tuff, and Carpenter Ridge Tuff.
Today, Quaternary silts, sands, and gravels are preserved in the canyons and surface depressions of Black Canyon- Curecanti as terrace deposits, alluvium, and colluvium. They represent only a fraction of the deposits that once spread across this area, only to be subsequently stripped from the region by the relentless process of erosion.
Cave and Karst
There are no known caves in the park, but the potential for small caves and shelters in the Jurassic and Cretaceous sandstones, siltstones, and shale exists. Minor karst potential also exists in these same rock units.
All NPS cave resources are protected under the the Federal Cave Resources Protection Act of 1988 (FCRPA)(16 U.S.C. § 4301 et seq.).
Geology Field Notes
Students and teachers of college-level (or AP) introductory geology or earth science teaching courses will find that each park's Geologic Resource Inventory report includes the Geologic History, Geologic Setting, and Geologic Features & Processes for the park which provides a useful summary of their overall geologic story. See Maps and Reports, below.
Black Canyon of The Gunnison National Park is a part of the Colorado Plateaus Physiographic Province, near its indistinct boundary with the Southern Rocky Mountains Physiographic Province to the east, and the park shares its geologic history and some characteristic geologic formations with regions that extend well beyond park boundaries.
Geologic Resources Inventory
- Scoping summaries are records of scoping meetings where NPS staff and local geologists determined the park’s geologic mapping plan and what content should be included in the report.
- Digital geologic maps include files for viewing in GIS software, a guide to using the data, and a document with ancillary map information. Newer products also include data viewable in Google Earth and online map services.
- Reports use the maps to discuss the park’s setting and significance, notable geologic features and processes, geologic resource management issues, and geologic history.
- Posters are a static view of the GIS data in PDF format. Newer posters include aerial imagery or shaded relief and other park information. They are also included with the reports.
- Projects list basic information about the program and all products available for a park.
Black Canyon Of The Gunnison National Park
National Park Service Geodiversity AtlasThe servicewide Geodiversity Atlas provides information on geoheritage and geodiversity resources and values within the National Park System. This information supports science-based geoconservation and interpretation in the NPS, as well as STEM education in schools, museums, and field camps. The NPS Geologic Resources Division and many parks work with National and International geoconservation communities to ensure that NPS abiotic resources are managed using the highest standards and best practices available.
For more information on the NPS Geodiversity Atlas, contact us.