By Melissa Stefos, 2002
Yellowstone National Park is located in Wyoming, Idaho and Montana and covers approximately 2,221,766 acres, which is roughly the size of Connecticut. It was established as a national park March 1, 1872 making it the world's first national park (NPS). Yellowstone is a great place for people of all ages to visit. Yellowstone is known for its beautiful scenery; unique animals including moose, elk and bears; its variety of vegetation; and its geysers and hot springs.
Yellowstone developed over millions of years into the wonder it is today. The park has rocks from the Pre-Cambrian basement, which includes gneisses and schists. Rocks from different ages can be found throughout the park. To see the Stratigraphic Column for Yellowstone National Park, please click here for MSWord or here PDF.
The Paleozoic Erathem contains mostly limestones, dolomites, sandstones and shales. Some major formations in the Paleozoic include The Meagher Limestone, Bighorn Dolomite, Madison Limestone, and Shedhorn Sandstone.
The Mesozoic Erathem has all sandstones and shales until the Late Cretaceous. Major formations during the Mesozoic include the Ellis Formation and Mowry Shale. There was a significant accumulation of basaltic lava flows and andesitic tuffs occurring in the northwestern part of the park during the Late Cretaceous continuing into the Cenozoic Erathem.
The Cenozoic Erathem is the most important part of Yellowstone to laypeople because those rocks are the most accessible and visible. Volcanic activity became dominant during this time as opposed to a marine environment (Christiansen, 2001).
The Eocene Stage includes the Absaroka Volcanic Supergroup, which contains the Sepulcher Formation. This formation is known for the fossil trees that are found at Specimen Ridge. These rocks are dominantly light colored andesites and volcaniclastics .
The Early Pleistocene welded tuffs in this area are especially important because they make up a huge portion of the whole area. Surficial geology of Yellowstone is composed of glacial deposits and three main tuffs from volcanic events beginning approximately 2.1 million years ago. The first welded tuff is the Huckleberry Ridge Tuff followed by the Mesa Falls Tuff (1.3 my) and the Lava Creek Tuff (.65my). The eruptions that caused these tuffs were immense.
The first eruption (Huckleberry Ridge) exploded 2,400 times as much rock as the 1980 Mt. St. Helens eruption. The ash from this first eruption goes as far west as California, east as Iowa, and north to Saskatchewan, and south to the Gulf of Mexico (Christiansen, 2001).
The second eruption came from the Island Park caldera and created the Mesa Falls Tuff 1.3 million years ago. This is the smallest of the three eruptions and actually lies in the Huckleberry Ridge Caldera.
The third eruption (Lava Creek) was also quite large as it covers parts of Huckleberry Ridge and it ruined parts of the Washburn Range. The Lava Creek caldera actually started to evolve 1.2 million years ago when the magma started rising to create a bulge with tons of fractures. The rhyolitic flow created ring fractures all around the caldera. These fractures went straight into the magma chamber where it started to relieve the pressure by having three eruptive pulses 150,000 years ago, 110,000 years ago and 70,000 years ago. The total rhyolitic rock produced covers about 240 cubic miles (Christiansen, 2001).
The top layer of the park consists mainly of different types of surficial and glacial deposits. During the Late Pleistocene, there were hydrothermal explosion deposits, hot spring deposits, cemented ice deposits and detrital deposits.
Christiansen, Robert, 2001. The Geology of Yellowstone National Park: The Quaternary and Pliocene Yellowstone Plateau Volcanic Field of Wyoming, Idaho, and Montana, USGS Professional Paper 729-G, 145p.
US Geological Survey, 1972, Geologic Map of Yellowstone National Park, Miscellaneous Geologic Investigations MAP I-711.
National Park Service, The Yellowstone National Park Web-page http://www.nps.gov/yell/
Yellowstone National Park www.yellowstonenationalpark.com