Wasatch Formation facts for kids

Quick facts for kids Wasatch Formation Stratigraphic range: Early Eocene (Clarkforkian-Bridgerian) (typically Wasatchian) ~56.8–46.2Ma PreЄ Є O S D C P T J K Pg N
Clinker-bed breccia from the Wasatch Formation (Wyoming)
Type	Formation
Sub-units	See text
Underlies	Green River & Fowkes Formations, Santa Fe Group
Overlies	Fort Union, Williams Fork, Torrejon & Evanston Formations
Thickness	Variable, up to 1,500 m (4,900 ft)
Lithology
Primary	Mudstone, shale, siltstone, sandstone
Other	Claystone, lignite
Location
Coordinates	41°12′N 108°48′W / 41.2°N 108.8°W / 41.2; -108.8
Approximate paleocoordinates	46°00′N 92°36′W / 46.0°N 92.6°W / 46.0; -92.6
Region	Colorado  Idaho  Montana  New Mexico  Wyoming  Utah
Country	United States
Extent	Powder River, Green River, Wind River, Bighorn, Piceance & Uinta Basins
Type section
Named for	Wasatch Range
Named by	Hayden
Location	Echo Canyon, Summit County & Weber Canyon, Ogden, Utah
Year defined	1873
Coordinates	40°53′N 110°58′W / 40.88°N 110.97°W / 40.88; -110.97 (Echo Canyon) 41°08′09″N 111°54′14″W / 41.13583°N 111.90389°W / 41.13583; -111.90389 (Weber Canyon)
Region	Utah

The Wasatch Formation is a huge rock layer found in many parts of the western United States. It stretches across Idaho, Montana, Wyoming, Utah, and western Colorado. This formation is super important because it holds many fossils from the Early Eocene time period, which was about 56.8 to 46.2 million years ago.

Scientists use the Wasatch Formation to help define a specific time in Earth's history called the Wasatchian age. During this period, many different kinds of animals lived, including early primates, hoofed animals like artiodactyls and perissodactyls, rodents, and carnivora (meat-eaters). We also find fossils of birds, reptiles, fish, and even tiny invertebrates. Besides animal remains, the formation also contains plant fossils and trace fossils, which are things like ancient footprints or burrows.

The Wasatch Formation was first named in 1873 by Ferdinand Vandeveer Hayden. It formed in areas where rivers flowed, floods happened, and lakes existed. The rocks are made of sandstones, siltstones, mudstones, and shales. It also has layers of coal or lignite, which show that parts of these ancient floodplains were wet and swampy.

Today, the Wasatch Formation is important for energy. It contains "tight gas," a type of natural gas that is hard to get out of the rock. People also mine coal from it in Wyoming. At the Fossil Butte National Monument, you can see the Wasatch Formation rocks right below the famous Green River Formation.

What is the Wasatch Formation?

How it was named

The Wasatch Formation was first called the Wasatch Group by Ferdinand Vandeveer Hayden in 1873. He studied rocks in the Echo and Weber Canyons, which are near the Wasatch Mountains. The name "Wasatch" comes from the Ute people's language and means "mountain pass." Another idea is that it comes from a Shoshone leader named wasattsi, meaning "blue heron."

Where to see the rocks

View of Fossil Butte with the Wasatch Formation outcropping in the lower areas

You can see the Wasatch Formation at the bottom of Fossil Butte National Monument. The rocks here are bright red, purple, yellow, and gray. They gently slope up from the valley. Above them are the lighter-colored rocks of the Green River Formation. The Wasatch Formation can be very thick, up to about 4,900 feet (1,500 meters) in some places. It's also visible in Desolation Canyon and Gray Canyon in Utah, and at Flaming Gorge National Recreation Area.

Where the formation is found

Map of the Powder and Wind River and Bighorn Basins

Map of the Green River Basin

Map of the Uinta and Piceance Basins

The Wasatch Formation is found in six states: Montana, Idaho, Utah, Wyoming, Colorado, and New Mexico. It's part of several large geological areas, including the Wasatch Range, Uinta Mountains, Green River, Piceance, Powder River, and Uinta Basins. In Montana, the Wasatch Formation sits on top of the Fort Union Formation.

Layers of the Wasatch Formation

Generalized stratigraphy of the Wasatch Formation

The Wasatch Formation is made of many smaller layers, or "members," that have their own names. These layers can be different in different places. Here are some of the named members:

What the rocks are made of

In Wyoming, the Wasatch Formation mostly has colorful mudstones. It also has layers of siltstones, sandstones, and conglomerates. These rocks formed on a wide plain between mountains. In Colorado, the formation has purple, red, and gray claystones and shales. It also has lenses of sandstones that came from rivers and lakes.

The Molina Member is a part of the formation with more sand. It formed when changes in the Earth's crust or climate caused a lot of sand to be washed into the basin. This sandy layer is important for finding natural gas.

Where the rocks came from

Scientists study tiny mineral grains called zircons in the Wasatch Formation. These zircons tell us where the sand and mud came from. Most of the grains are very old, about 2.9 billion years old. This matches the age of rocks in the core of the Bighorn Mountains. This means the Bighorn Mountains were eroding and shedding sediment into the area when the Wasatch Formation was forming. The presence of the Kingsbury Conglomerate at the bottom of the formation shows that the Earth's crust was very active nearby.

Why the Wasatch Formation is important for fossils

The Wasatch Formation is key to understanding the Wasatchian age, which lasted from about 55.8 to 50.3 million years ago. This time period is special because it marks the first appearance of many new types of mammals, including early primates and hoofed animals. The formation was laid down during a time when Earth was very warm, known as the Paleocene-Eocene Thermal Maximum (PETM). The average temperature was around 77°F (25°C).

At Fossil Butte National Monument, the Wasatch Formation has preserved trace fossils made by arthropods (like insects or crabs). These include burrows and tracks. These traces show how animals lived in different environments, like floodplains and river channels.

Animals found in the Wasatch Formation

Many amazing fossils have been found here!

Mammals

Primates

Hoofed Animals (Artiodactyls and Perissodactyls)

Meat-eaters (Carnivora and Hyaenodonta)

Rodents (Glires)

Other Mammals

Birds

Reptiles

Amphibians

• Caudata indet. (ancient salamanders)

Fish

Invertebrates

Bivalves

Gastropods

Flora (Plants)

Trace Fossils

Herbivore expansion

The many plant-eating mammals found in the Wasatch Formation are part of a big increase in herbivores that happened over millions of years. This "herbivore expansion" is also seen in other rock formations from the same time.

Economic uses of the Wasatch Formation

Natural gas

The Wasatch Formation is a source of "tight gas" in Utah and Colorado. This means the gas is trapped in very dense rock. It's harder to get out than regular gas, but new methods help. Many wells have been drilled, producing trillions of cubic feet of gas.

Mining

Coal

Thick layers of coal are mined from the Wasatch Formation in Wyoming. These coal beds are some of the thickest in the state.

Uranium

The sandstones in the Wasatch Formation also contain uranium deposits. This formation is the main source of uranium in Wyoming. The uranium is found in minerals like uraninite.

Related Formations

The Wasatch Formation is connected to other rock formations from the same time period. Scientists compare the fossils and rock types to understand ancient environments across North America.

Wasatchian correlations in North America

Formation	Wasatch	DeBeque	Claron	Indian Meadows	Pass Peak	Tatman	Willwood	Golden Valley	Coldwater	Allenby	Kamloops	Ootsa Lake	Margaret	Nanjemoy	Hatchetigbee	Tetas de Cabra	Hannold Hill	Coalmont	Cuchara	Galisteo	San Jose	Ypresian (IUCS) • Itaboraian (SALMA) Bumbanian (ALMA) • Mangaorapan (NZ)
Basin	Powder River Uinta Piceance Colorado Plateau Wind River Green River Bighorn	Piceance	Colorado Plateau	Wind River	Green River	Bighorn		Williston	Okanagan	Princeton	Buck Creek	Nechako	Sverdrup	Potomac	GoM	Laguna Salada	Rio Grande	North Park	Raton	Galisteo	San Juan
Country	United States								Canada					United States		Mexico	United States
Copelemur
Coryphodon
Diacodexis
Homogalax
Oxyaena
Paramys
Primates
Birds
Reptiles
Fish
Insects
Flora
Environments	Alluvial-fluvio-lacustrine	Fluvial				Fluvial	Fluvio-lacustrine	Fluvial	Lacustrine		Fluvio-lacustrine		Deltaic-paludal	Shallow marine		Fluvial	Shallow marine	Fluvial		Fluvial		Wasatchian volcanoclastics Wasatchian fauna Wasatchian flora
Volcanic	Yes	No							Yes	No	Yes	No	Yes	No						Yes	No