Fossils & Paleontology

Did You Know?

Geology and paleontology are together one of the fundamental resources and values identified in the park's foundation document. Geologic features provide the scenic backdrop for the three reservoirs and reveal the evidence of Late Jurassic and Early Cretaceous environments.

 

 

Since the 1990s, various paleontological surveys have been conducted in Curecanti. Most of the paleontological resources at Curecanti are from the Jurassic, Cretaceous, and Pleistocene-Holocene periods. These include fossil plants, invertebrates, vertebrates, and trace fossils. These fossils are part of the park and surrounding area’s geologic story.

Changing reservoir levels and annual runoff cause weathering an erosion. This leads to an increased concern for the preservation of paleontological resources. The following laws protect all fossil found in national parks. Please leave everything you find as it is.

 

Early Cretaceous pinecone

NPS

Types of Fossils

Becoming a fossil is rare. Fossils require ideal conditions, such as being buried or living in water. Paleontologists find more fossils of small marine organisms instead of larger mammals or dinosaurs.

Vertebrate Fossils

Vertebrate fossils are parts of the body of anything with a backbone (bones, teeth, armor, soft tissue impressions). This includes the dinosaurs that called this area home long ago. Most dinosaur fossils are found where ancient rivers, lakes, and swamps were. Water was able to move enough sediment to bury the dinosaur remains - therefore beginning the fossilization process. Dinosaur, reptile, amphibian, bird, and mammal bones have been found at Curecanti from the Jurassic to Pleistocene-Holocene.

Plant Fossils

Plant fossils can include flowers, trees, stumps, leaves, roots, nuts, cones, needles, stems, twigs, seeds, and pollen. Fossil wood, plant fragments, leaf impressions, and root traces have been found in different sandstone formations at the park.

Invertebrate Fossils

Invertebrate fossils are fossils from organisms without backbones or a segmented spinal column. This includes animals with internal or external shells, snails, insects, and spiders. These types of fossils are the most encountered in national parks. Curecanti has invertebrate fossils from both the Jurassic and Cretaceous periods.

Trace Fossils

Trace fossils are traces of something an animal or plant did during its life. These behaviors or activities are like snapshots of how the animal or plant lived. These types of fossils include footprints and trackways, burrows, marks from feeding, scat (coprolites), and even diseases. There have been a root traces and burrows found at Curecanti.

 

Fossil Record at Curecanti

Although some formations may not contain paleontological resources at Curecanti, there may be examples found in the same layer at other national parks. Due to the terrain being heavily eroded, covered with thick vegetation, or impacted by the creation of Blue Mesa Reservoir, some typically fossil rich formations cannot be surveyed to the greatest extent.

Precambrian

The oldest exposed rocks at Curecanti are Precambrian metamorphic and igneous rocks. It is hard to tell what the paleo-environment was like from metamorphic rocks, since they have been changed dramatically over time. These metamorphic processes can squish or destroy fossils. This makes fossils unlikely to be found.

Middle Jurassic

The environment during the Middle Jurassic ranged from a desert with large sand dunes to something more marine-like. Entrada Sandstone, a fine to medium coarse-grained sandstone, is from this age. In sandy deserts, bones break down quicker, and wind sweeps away footprints. The Wanakah Formation includes more siltstone and mudstone with fine grained cross bedding. This aligns more with the marine depositional environment. This formation is not famous for fossils. However, some invertebrate burrows and a plant mold have been found along the North Rim Road.

 

Vertebra mold in the Late Jurassic Morrison Formation

NPS

Middle Jurassic

The environment during the Middle Jurassic ranged from a desert with large sand dunes to something more marine-like. Entrada Sandstone, a fine to medium coarse-grained sandstone, is from this age. In sandy deserts, bones break down quicker, and wind sweeps away footprints. The Wanakah Formation includes more siltstone and mudstone with fine grained cross bedding. This aligns more with the marine depositional environment. This formation is not famous for fossils. None have been found at Curecanti.

Late Jurassic

The Morrison Formation at Black Canyon and Curecanti is divisible into members, such as the Salt Wash and Brushy Basin members. These date back between 155 and 148 mya. This formation is well-known for its fossils. Large dinosaurs such as Allosaurus, Apatosaurus (often called "Brontosaurus"), Brachiosaurus, Diplodocus, and Stegosaurus are well known from the Morrison. Outcrops of the Morrison Formation can be difficult to access due to terrain or being now underwater. Despite this challenge, many vertebrate and invertebrate trace fossils have been found.

Most large trace fossils are on large sandstone boulders along Blue Mesa Reservoir. Other fossils in the Morrison Formation here are invertebrate burrows, bones of turtles, reptiles, mammals, and fragments of dinosaur teeth, vertebrate, and limb bones. Fossils were collected from beach sites to protect them from vandalism or heavy erosion. These discoveries, information, and ongoing research help scientists understand ancient ecosystems and the diverse life that existed here during the Jurassic.

 

A bivalve in the Mancos Shale at Cimarron

NPS

Early to Late Cretaceous

Burro Canyon Sandstone, Dakota Sandstone, and Mancos Shale are all formations from the Early to Late Cretaceous. The Burro Canyon Sandstone has no recorded fossils in the park.

The Dakota Sandstone is made up of sandstone and shale. It is more erosion resistant than the Mancos Shale. Fossils in this formation are diverse due to a variety of deposition across environments. Plant fragments, wood, molds of plant and invertebrate fossils, and invertebrate burrows have been found in the park.

Late Cretaceous

Mancos Shale is a clay-rich shale layer with some sandstone and siltstone. It is known for being rich in marine fossils across the Colorado Plateau, even with how fast it breaks down. Within the park, bivalves (clams, oysters, and ammonites), plant fragments, invertebrate traces and fragments of fish have been found.

 

Stratigraphy and Fossils Chart

Some formations/rocks are included to show areas where fossils are improbable or have not found in the park.

 

Age	Million Years Ago (mya)	Formation/Rock Layer	Geologic Features	Erosion Resistance	Rock Formation Environment	Paleontological Resources
Pleistocene-Holocene	1.8 to 0.01 mya	Surface deposits	Sands, silts, clays, pebbles, gravel	Low	Floodplain, river deposits, volcanic ash, landslides, wind activity/erosion	Bones of reptiles, amphibians, birds, and mammals, packrat middens, dens, pollen, and nests
Oligocene	34 to 23 mya	West Elk Breccia/San Juan Tuff	Volcanic ash deposits	Moderate	Volcanic ash, volcanic landslides, some river deposits	None found at the park
Late Cretaceous	99 to 65 mya	Mancos Shale	Silty clay shale	Low	Open marine environment	Plant fragments, bivalves, invertebrate traces, and fragments of fish
Early to Late Cretaceous	144 to 65 mya	Dakota Sandstone	Medium to coarse grained sandstone	Moderate to high	River deposits, shallow marine environment	Plant fragments, wood, molds of plant and invertebrate fossils, and invertebrate burrows
Early Cretaceous	144 to 99 mya	Burro Canyon Sandstone	Medium to coarse grained sandstone	Moderate to high	River and lake environments, floodplains	None found at the park
Late Jurassic	161 to 145 mya	Morrison Formation	Mudstone, siltstone, sandstone	Low to moderate	River and lake environments, floodplains	Sauropods, bones of reptiles, mammals, invertebrate burrows, and other trace fossils
Middle Jurassic	174 to 162 mya	Wanakah Formation	Mudstone, siltstone, sandstone	Moderate to high	Marine environment becoming sand dunes made by wind	None found at the park
Middle Jurassic	174 to 162 mya	Entrada Sandstone	Fine to medium grained sandstone	High	Desert with sand dunes made by wind	None found at the park
Precambrian	4.5 billion to 541 mya	Basement rocks	Metamorphic and igneous rock, pegmatites	High	N/A	None found at the park

More on Geology and Fossils

 

 

Resources

Koch, A. L., Frost, F. and K.C. Trujillo. 2006. Paleontological discoveries at Curecanti National Recreation Area and Black Canyon of the Gunnison National Park, Upper Jurassic Morrison Formation, Colorado. Pages 35-38 in Foster, J. R. and S. G. Lucas, editors. Paleontology and geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science, Albuquerque, NM. Bulletin 36.

Thornberry-Ehrlich T. 2005. Black Canyon of the Gunnison National Park & Curecanti National Recreation Area Geologic Resource Evaluation Report. Natural Resource Report. NPS/NRPC/GRD/NRR—2005/001. NPS Geologic Resources Division. Denver, Colorado https://irma.nps.gov/DataStore/Reference/Profile/644341

Trujillo, K. 2000. Dino Cove Paleontological Investigations, 1994-1999, Curecanti National Recreation Area: Curecanti National Recreation Area Report, 1-21.

Tweet JS and Others. 2012. Paleontological resource inventory and monitoring: Northern Colorado Plateau Network. Natural Resource Technical Report. NPS/NCPN/NRTR—2012/585. National Park Service. Fort Collins, Colorado https://irma.nps.gov/DataStore/Reference/Profile/2185278