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Heart Mountain

World’s Largest Continental Landslide

Mountain on Mountain Trail in Rocky Mountains near Cody, WY

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SUMMARY

Heart Mountain is an instantly recognizable mountain near Cody and Powell that is notable for its geological uniqueness. The limestone peak stands out from its flat surroundings, and the rock layers are flipped – the oldest layers are on top instead of bottom. It is also historically significant. In 1942 a major Japanese-American Internment Camp was built in the foothills and it housed over 10000 people throughout World War II. For more information there is the nearby Heart Mountain Interpretive Center.The summit is easily accessed via a trail that switchbacks up the mountain starting at Heart Mountain Trailhead.

PHOTOGRAPHS

GEOLOGY SECTION

PRECAMBRIAN GEOLOGY Age of Early Life

“Date range: 4,540 million years ago (MYA) to 541 MYA

Length: 3,998 million years (88.1% of geologic time)

Geologic calendar: January 1 to November 19 (323 days)

Precambrian Summary: The Precambrian was the “Age of Early Life.” During the Precambrian, continents formed and our modern atmosphere developed, while early life evolved and flourished. Soft-bodied creatures like worms and jellyfish lived in the world’s oceans, but the land remained barren. Common Precambrian fossils include stromatolites and similar structures, which are traces of mats of algae-like microorganisms, and microfossils of other microorganisms.” (NPS, Geologic Time)

4,600 Million Years Ago (MYA)

As our primordial 4.6 billion year old molten Earth cooled, around 4 to 3.4 billion years ago the first rocks crystallized from the hot liquid. These igneous rocks formed the first crust of land, which grew in area and thickness becoming continental crust. Also evolving from cooling molten rocks, water vapor and other gases were released, creating an atmosphere around the planet.

3,800 MYA

About 3.8 billion years ago, when our atmosphere had cooled below 212 degrees Fahrenheit, rain fell upon the surface of the Earth. As igneous rock continued to form, existing rock started to deteriorate and crumble from erosional forces. These igneous rock pieces were then deposited in layer upon layer, becoming sedimentary rock. The Earth was forming plates of land and rain was filling the land basins, creating oceans.

Hot magma continually rose below continental plates. If it solidified below the surface, it formed an igneous intrusive or plutonic rock type like granite. If the magma pierced the land surface, an igneous extrusive rock like basalt (lava) and obsidian formed. Even the ocean floors started their own igneous rock assembly lines, where centerline ridges in the basins extruded magma that cooled into basalt rock, pushing and spreading out underwater plates of land.

3,000 MYA

As continental land and seafloor plates spread, accumulated in thickness, and collided with another, metamorphic rocks started forming from 3 to 2.5 billion years ago. Igneous and sedimentary rocks that made up the plates became buried deep enough, that intense pressure, heat, and hot chemical water altered them into rocks like slate, soapstone, marble, and gneiss. Igneous granite, and gneiss the metamorphosed version of granite, would eventually be raised up to form the Beartooth Mountains, the high country home of Heart Mountain, before it slide off into the Bighorn Basin.

2,500 MYA

Land created from 4 to 2.5 billion years ago was then roughly graded for the next 2 billion years by an erosional bulldozer into a flat slab. West of Cody, WY in the Shoshone Canyon, the sequence of layered rocks shows a 2 billion year gap, called the Great Unconformity. Wyoming’s slab of granite took 2 billion years to level, and now was ready to build upon.

PALEOZOIC ERA GEOLOGY

“Date range: 541 million years ago to 251.9 million years ago

Length: 289.1 million years (0.64% of geologic time)

Geologic calendar: November 19–December 12 (23 days)

Paleozoic Era Summary: In North America, the Paleozoic is characterized by multiple advances and retreats of shallow seas and repeated continental collisions that formed the Appalachian Mountains. Common Paleozoic fossils include trilobites and cephalopods, as well as insects and ferns. The greatest mass extinction in Earth’s history ended this era. The Paleozoic Era is subdivided into seven Periods the Cambrian, the Ordovician, the Silurian, the Devonian, the Mississippian, the Pennsylvanian, and the Permian.” (NPS, Geologic Time)

541.0 MYA begins the Cambrian Period of the Paleozoic Era

“Date range: 541 MYA to 485.4 MYA

Length: 55.6 million years (1.2% of geologic time)

Geologic calendar: November 19–November 23 (Noon) (4 days, 12 hours)” (NPS, Geologic Time)

Around 541 million years ago, Wyoming was on the western coastline of the early North American continent, and a shallow western Cambrian sea covered most of the state. The warm sea, deposited sandstones, shales, limestones and a fossil record of trilobites, segmented worms, algae, corals, and sponges. The sequence formations built upon the granite slab started with the Flathead sandstone, an ancient beach, followed by sedimentary layers of Park shale, Pilgrim limestone, and the Snowy Range formation. At the end of Cambrian time, the sea retreated from most of Wyoming, subjecting the dry land to erosional forces again, creating another unconformity or gap in the geological record.

485.4 MYA begins the Ordovician Period of the Paleozoic Era

“Date range: 485.4 million years ago to 443.8 million years ago

Length: 41.6 million years (0.92% of geologic time)

Geologic calendar: November 23 (Noon) – November 26 (7 PM) (3 days, 7 hours)” (NPS, Geologic Time)

With most of Wyoming above sea level, sometime starting around 485.4 million years ago, the eroded land subsided, and an Ordovician sea covered the land. New marine life, like torpedo shaped cephalopods (squids), flowering sea lilies called crinoid plants with their star-shaped stacked segmented stems, and jawless armored fish lived beneath the waves until leaving their fossils in a thick formation of Bighorn dolomite. Sea level fell again and with the warm water retreating and exposing land to erosion, the Bighorn’s uppermost section was eroded away. However, in the vast sheet of the Bighorn dolomite that survived, a future landslide block of it would create the top portion of Heart Mountain that rests on top of a 55 million year old mountain base of mudstone, shale, sandstone, and conglomerate.

443.8 MYA begins the Silurian Period of the Paleozoic Era

“Date range: 443.8 million years ago to 419.2 million years ago

Length: 24.6 million years (0.54% of geologic time)

Geologic calendar: November 26 (7 PM) – November 28 (6 PM) (1 day, 23 hours)” (NPS, Geologic Time)

In Wyoming, the Silurian Period was a time of uplift and erosion. There are no Silurian rocks or fossils in Wyoming to document the world ushering in the “Age of Fishes”.

419.2 MYA begins the Devonian Period of the Paleozoic Era

“Date range: 419.2 million years ago to 358.9 million years ago

Length: 60.3 million years (1.3% of geologic time)

Geologic calendar: November 28 (6 PM) – December 3 (1 PM) (4 days, 19 hours)” (NPS, Geologic Time)

Beginning 419.2 million years ago, the sea returned across western and northern Wyoming, continuing the “Age of Fishes”. In the northwest, marine formations of the Beartooth Butte’s red siltstones, the Jefferson’s yellow-orange dolomites and siltstones, topped with the Three Forks’ greenish gray siltstones and black shale, were added. Marine life developed as primitive fish grew jaws and replaced their jawless predecessors, and amphibians appeared.

358.9 MYA begins the Mississippian Period of the Paleozoic Era

“Date range: 358.9 million years ago–323.2 million years ago

Length: 35.7 million years (0.8% of geologic time)

Geologic calendar: December 3 (1 PM) – December 6 (9 PM) (3 days, 8 hours)” (NPS Geologic Time)

By 358.9 million years ago, during the “Age of Crinoids” commonly called “sea lilies”,all of Wyoming was underwater and the massive gray Madison limestone was deposited. Later uplifting and exposure eroded the Madison top away, leaving its signature cavernous surface depressions. The Madison limestone forms the skyline summit and the sheer cliff face of Heart Mountain.

323.3 MYA begins the Pennsylvanian Period of the Paleozoic Era

“Date range: 323.2 million years ago–298.9 million years ago

Length: 24.3 million years (0.54% of geologic time)

Geologic calendar: December 6 (9 PM) – December 8 (7 AM) (1 day, 10 hours)” (NPS Geologic Time)

In northwestern Wyoming’s Pennsylvanian Period, shallow seas transgressed and regressed started 323.3 million years ago depositing limestones and sandstones sections of the Amsden Formation. Later regional uplift allowed a Sahara like desert to claim land from the shallow sea and, with prevailing north wind out of Canada and Montana, laid down a thick blanket of sand dunes that became the Tensleep Formation.

298.9 MYA begins the Permian Period of the Paleozoic Era

“Date range: 298.9 million years ago–251.9 million years ago

Length: 47 million years (1.0% of geologic time)

Geologic calendar: December 8 (7 AM) – December 12 (1 AM) (3 days, 18 hours)

Permian Period Summary: Earth’s crustal plates formed a single, massive continent called Pangaea. In the correspondingly large ocean, Panthalassa, marine organisms such as brachiopods, gastropods, cephalopods (nautiloids and ammonoids), and crinoids were present. On land, reptiles replaced amphibians in abundance. The most devastating incidence of mass extinction in Earth’s history marked the end of the Permian Period.” (NPS Geologic Time)

After millions of years of sand deposition, starting around 298.9 million years ago, the sea moved back over Wyoming and created the Permian Period gray colored phosphatic Phosphoria Formation topped with the Dinwoody Formation. For about 50 million years, life flourished in Wyoming with marine plants and animals like corals, squid like cephalopods called belemnites, as well as snails and slugs. On land, reptiles and coniferous trees appeared.

A life bearing sea retreated from Wyoming close to 251.9 million years ago, and a mass extinction marked the end of the Permian -“ far more devastating than the more famous Cretaceous extinction when the dinosaurs disappeared… Scientists estimate that more than half (53%) of all taxonomic families were lost. This translates to 95% of all species, including 70% of all land species (i.e., plants, animals, and insects). The cause may have been climate change resulting in a worldwide lowering in sea level… The Permian mass extinction came closer than any other extinction event in the fossil record to wiping out life on Earth.” (NPS Geologic Time)

MESOZOIC ERA Age of Reptiles

“Date range: 251.9 million years ago–66.0 million years ago

Length: 185.9 million years (4.1% of geologic time)

Geologic calendar: December 12 (1 AM) – December 26 (6 PM) (14 days, 17 hours)

Mesozoic Era Summary: During the Mesozoic, Pangaea began separating into the modern continents, and the modern Rocky Mountains rose. Dinosaurs, crocodiles, and pterosaurs ruled the land and air. As climate changed and rapid plate tectonics resulted in shallow ocean basins, sea levels rose world-wide and seas expanded across the center of North America. Large marine reptiles such as plesiosaurs, along with the coiled-shell ammonites, flourished in these seas. Common Mesozoic fossils include dinosaur bones and teeth, and diverse plant fossils. The Mesozoic Era is subdivided into three Periods, the Triassic, the Jurassic, and the Cretaceous.” (NPS, Geologic Time)

251.9 MYA begins the Triassic Period of the Mesozoic Era

Date range: 251.9 million years ago–201.3 million years ago

Length: 51.4 million years (1.1% of geologic time)

Geologic calendar: December 12 (1 AM) – December 16 (1 AM) (4 days)

When the sea returned to Wyoming and fluctuated across the land or whatever remained of the prior Permian sea, it was a comparatively “dead sea”. From 251.9 to 201.3 million years ago, during the Triassic red bed period, successive massive dust storms blew in red silt and fine red sand that settled down over a very shallow, still, and vast sea with wide tidal flats forming layers of vibrant red Chugwater Formation that contains hardly any fossils. The Triassic Period began with Pangaea starting to break apart. The Triassic ended someway with mass extinction, possibly a single event or smaller extinction events that occurred throughout this geologic period. Looking west from Cody, WY, the Chugwater red beds of Red Butte are visible along the base of Rattlesnake Mountain.

201.3 MYA begins the Jurassic Period of the Mesozoic Era

“Date range: 201.3 million years ago–145.0 million years ago

Length: 56.3 million years (1.2% of geologic time)

Geologic calendar: December 16 (1 AM) – December 20 (12 Noon) (4 days, 11 hours)

Jurassic Period Summary: Start of the golden Age of Dinosaurs.” (NPS, Geologic Time)

Wyoming’s Jurassic times of 201.3 to 145 million years ago started with a retreating sea, leaving a large confined shallow basin in a hot dry climate. Layers of soft gypsum rock, the Gypsum Spring Formation materialized in the lagoons when the marine waters high in calcium and sulfate content slowly evaporated. Then a shallow Sundance sea periodically washed over and back across the land, followed by an explosion of dinosaur life on the broad floodplains of the infamous Morrison Formation. Southern Wyoming’s famous Como Bluff is a Morrison Formation dinosaur grave yard.

On the world scene, Jurassic time continued with the breakup of the supercontinent Pangaea as North America and its fellow continents split apart. The Atlantic Ocean begins and grows wider as lava pours out from the center of the ocean floor. North America shifted northward, resulting in the formation of vast deserts and, at other times, flooding the land with shallow seas. In the latter part of the Jurassic Period, the landscape transformed from deserts and shallow seas into vast floodplains that supported an array of life forms, including dinosaurs.

During Morrison times, ferns, cycads, and horsetails carpeted the land, as stands of conifer trees, ginkgoes, and tree ferns grew tall. The landscape was lush green, as plants had not developed flowers yet. Rivers and lakes supported fish, turtles, crocodiles, and mussels. Immense dinosaurs, long-necked Apatosaurus/Brontosaurus, Diplodocus, Brachiosaurus, and the plated Stegosaurs, roamed and grazed the floodplain while avoiding the carnivorous dinosaur Allosaurus. Much smaller amphibians, lizards, and mammals, foraged around these giants, while insects and Pterosaurs flew by.

170 MYA begins the Sevier Orogeny of Overthrust Mountain Building

As a dense oceanic crust beneath the Pacific Ocean, the Farallon plate converged with, and slid beneath, the more buoyant continental crust of the North American mountain building episodes started across western North America.

As the denser Farallon plate slide below the continental crustal plate, it sent pulses of mountain building shockwaves from west to east across North America. The first mountain building event, the Sevier Orogeny roughly 170-40 million years ago caused the overthrust belts of Utah and along the Utah- Wyoming border.

145 MYA begins the Cretaceous Period of the Mesozoic Era

“Date range: 145.0 million years ago–66.0 million years ago

Length: 79 million years (1.7% of geologic time)

Geologic calendar: December 20 (12 Noon) – December 26 (6 PM) (6 days, 6 hours)

Cretaceous Period Summary: The first flowering plants appeared and rapidly diversified. The Rocky Mountains began to rise from the Cretaceous Interior Seaway. The Cretaceous ended with a mass extinction of all the dinosaurs when a large asteroid crashed into Earth near the Yucatan Peninsula of Mexico.” (NPS, Geologic Time)

From a continental perspective, the Cretaceous Period of North America had several distinct phases:

First Third to Half of the Period: the paleogeographic world resembled Late Jurassic’s broad floodplains. The dinosaurs of the Early Cretaceous, before the Western Interior Seaway developed, are a mix of Jurassic-like holdovers and newer forms. The long, low Diplodocus-like sauropods and the plated stegosaurs went extinct; while ankylosaurs and ornithopods diversified; and sickle-clawed theropods became significant small carnivores. North America was close to its current position regarding latitude and longitude. However, the Wyoming core landmass is now going to be shape shifted by compression and mountain building called orogeny.

Halfway through the Cretaceous Period: rising sea levels from the breakup of Pangaea and mountain building, submerged the shallow sediment heavy lowlands of the center of the continent. While the Sevier Orogeny thrust the western margin up into an Andes like mountain range the compressed land mass to the east warped down into the plastic like lithosphere below forming a sunken forebasin that filled with water. North America became two continents at this time, a narrow western mountainous continent and a broader eastern continent, divided by a Western Interior Seaway. We know little about the dinosaurs that lived in North America during the height of the Western Interior Seaway, although there are many fossils of marine reptiles and pterosaurs in the marine rocks.

80 MYA begins the Laramide Orogeny of Rocky Mountain Uplift

Late Cretaceous times around 80-70 million years ago: Wyoming’s Rocky Mountains with the Laramide Orogeny pushed up from broader eastern continent. The interior sea retreated and North America was one continent again. Dinosaurs reclaimed the land left by the retreating interior sea. The dinosaurs at the end of the Cretaceous in North America are some of the best known in the world. In Wyoming, these dinosaurs were Tyrannosaurus rex, Triceratops (the Wyoming State Dinosaur), Anatosaurus, and Ankylosaurs among the now dominant deciduous trees (beech, birch, maple, oak, and walnut).

66 MYA Dinosaur Cretaceous Mass Extinction

End of the Cretaceous: is famously marked by a major extinction that killed off all dinosaurs except birds, many groups of early birds, pterosaurs, marine reptiles, shelled squid-like ammonites, and many other groups, this extinction is possibly from the Chicxulub meteorite impact near the Yucatan Peninsula of Mexico .

CENOZOIC ERA Age of Mammals

“Date range: 66.0 million years ago – Today

Length: 66.0 million years (1.5% of geologic time)

Geologic calendar: December 26 (6 PM) – December 31 (Midnight) (5 days, 6 hours)

Cenozoic Era Summary: Today’s North American landscapes began to develop during the Cenozoic ERA. Birds and mammals rose in prominence after the extinction of giant reptiles. Common Cenozoic fossils include cat-like carnivores and early horses, as well as ice age woolly mammoths. The Cenozoic Era is subdivided into three Periods: the Paleogene, the Neogene, and the Quaternary.” (NPS, Geologic Time)

66 MYA begins the Paleogene Period of the Cenozoic Era

“Date range: 66.0 million years ago–23.0 million years ago

Length: 43.0 million years (0.95% of geologic time)

Geologic calendar: December 26 (6 PM) – December 30 (4 AM) (3 days, 10 hours)

The end of Mesozoic Era’s Age of the Reptiles began the Cenozoic Era’s Age of the Mammals 66 million years ago. Three Periods, oldest to youngest, make up the Age of Mammals. The Paleogene Period, the oldest Period, is divided into three Epochs Paleocene, Eocene, and Oligocene.” (NPS, Geologic Time)

66 MYA begins the Paleocene Epoch of the Paleogene Period

Date range: 66.0 million years ago-56 million years ago

The Paleocene Epoch in northwestern Wyoming 66 MYA was a warm tropical time of late stage Laramide style Rocky Mountain building. Also during this time, the Absaroka Range volcanic belt was active. In the Bighorn basin, the Fort Union Formation’s coal beds were deposited, followed by the Willwood Formation’s fossiliferous sandstones, claystones, and shales laid down on an alluvial floodplain. The purple, green and red Willwood Formation in places up to 2,000 feet thick helped fill the Bighorn Basin and formed the base of Heart Mountain beneath the white peak. Looking east from Cody at the McCullough Peaks, the Willwood Formation’s red and white layers are visible.

56 MYA begins the Eocene Epoch of the Paleogene Period

Date range: 56.0 million years ago-33.9 million years ago

The Eocene Epoch started in a greenhouse climate and then transitioned to an icehouse climate, forcing tropical plants and animals to adapt or perish.

In southwestern Wyoming, of particular significance is the Eocene Green River Formation’s fossil fish, including Knightia, the Wyoming State Fossil. This formation was deposited on the floor of ancient Lake Gosiute part of which is now Fossil Butte National Monument.

53 to 43 MYA Absaroka Range Volcanos of the Eocene Epoch are active

In northwestern Wyoming, Eocene Absaroka volcanos dominated the landscape. The petrified forests of Yellowstone’s Specimen Ridge are from the Eocene Epoch and are a record of the earlier Absaroka volcanics, not the Yellowstone National Park calderas. Between 53 and 43 million years ago, Eocene volcanos added to the Absaroka Range in northwestern Wyoming and the Gallatin Range in southwestern Montana. Explosive volcanic centers, some containing several volcanoes, pierced the crust at points from Bozeman, MT to almost Dubois, WY. These steep sided, cone shaped volcanoes reached heights of 10 to perhaps 20 thousand feet above the land, creating a thick coating of volcanic rubble over a vast area. Volcanos Mount Washburn, Electric Peak-Sepulcher, Emigrant Peak, Independence, Point of Rocks and Hyalite pierced the earth’s crust along the WY-MT border; volcanos Crandall and Sunlight erupted northeast of Yellowstone; while Sylvan Pass, Rampart, Ishawooa, South Fork, and Kirwin erupted their way southeast towards present day Dubois, WY.

50 to 49 MYA Heart Mountain Landslide

Heart Mountain’s landslide was triggered about 50 to 49 million years ago, when a 450 to 500 square mile carbonate rock slab, 3 to 6 football fields thick broke loose from the collapsing side of an active volcano near Silver Gate, MT. Sliding on a cushion of carbon dioxide gas, like an air hockey puck, the slab traveled southeast at 335 miles per hour, over an almost horizontal 2 degree slope. Amidst volcanic debris, the massive sliding slab broke into smaller spinning blocks and dispersed those pieces to their ultimate resting places over a 1,300 square mile an area.

Cody’s Heart Mountain block traveled 30 miles up and over Dead Indian Hill to rest on the younger Willwood Formation. Another carbonate block traveled 13 miles further on to rest on McCullough Peaks. West of Cody, older carbonate blocks crown younger Cretaceous layers, at Sheep Mountain and Logan Mountain.

49 to 47 MYA Absaroka Range Volcanic Debris

In a landscape being volcanically created, reshaped, and reshuffled in monumental fashion by volcanism and erosion, there was more change to come. After the Heart Mountain landslide, during a 2 million year time span from 49 to 47 million years ago, about sixty percent of the Absaroka Range volcanic rubble pile was added to the land from active Absaroka volcanos.

HEART MOUNTAIN GEOLOGY EPILOGUE

Heart Mountain is one piece of a great puzzle, that geologists from around the world continue to study and try to understand. The entire puzzle is complicated, amazing, hard to believe, debatable, and far from compete. Puzzle pieces and clues scattered over a large area, and volcanic debris cluttered around and on top of the puzzle board complicates interpretations. The story of Heart Mountain is as epic as a tale from Jim Bridger or John Colter.

GEOLOGY PHOTOGRAPHS, MAPS and ILLUSTRATIONS

Image above from: Hauge, Thomas A. “The Heart Mountain Detachment, Northwestern Wyoming: 100 Years of Controversy.” In Geology of Wyoming, edited by A. W. Snoke, J. R. Steidtmann, and S. M. Roberts, 530–71. Memoir 5. Geological Survey of Wyoming, 1993. https://sales.wsgs.wyo.gov/geology-of-wyoming-1993/.

Geologic Time Scale shown above from NPS

Shown above a Map of the Heart Mountain slide block. From Mitchell et al., 2015 (“Catastrophic emplacement of giant landslides aided by thermal decomposition: Heart Mountain, Wyoming.” Earth and Planetary Science Letters 411: 199-207), modified from Anders et al. (2010).

With the northwestern breakaway point near Silver Gate, MT, the Heart Mountain slide block moved southeast toward Cody, WY (orange arrow). Notable deposits of the debris avalanche include White Mountain, Heart Mountain, and the McCulloch Peaks.

SOURCES

Aharonov, E., and Mark Anders. “Hot Water: A Solution to the Heart Mountain Detachment Problem?” Geology 34 (March 1, 2006). https://doi.org/10.1130/G22027.1.

Anders, Mark H., Bruce W. Fouke, Aubrey L. Zerkle, Enrico Tavarnelli, Walter Alvarez, and George E. Harlow. “The Role of Calcining and Basal Fluidization in the Long Runout of Carbonate Slides: An Example from the Heart Mountain Slide Block, Wyoming and Montana, U.S.A.” The Journal of Geology 118, no. 6 (September 2010): 577–99. https://doi.org/10.1086/656383.

Blakey, R.C., and W.D. Ranney. Ancient Landscapes of Western North America: A Geologic History with Paleogeographic Maps. eBook. Springer International Publishing, 2017.

Chadwick, Robert A. “Belts of Eruptive Centers in the Absaroka-Gallatin Volcanic Province, Wyoming-Montana.” GSA Bulletin 81, no. 1 (January 1, 1970): 267–74. https://doi.org/10.1130/0016-7606(1970)81[267:BOECIT]2.0.CO;2.

Craddock, John, and David Malone. “Recent Contributions to the Understanding of the Heart Mountain Detachment.” Northwest Geology, August 8, 2008. https://www.researchgate.net/publication/254617445_Recent_Contributions_to_the_Understanding_of_the_Heart_Mountain_Detachment.

Fisher, Mark P., Ken Steele, and Deb D. Steele. “Absaroka Volcanic Province.” Geology of Wyoming. Accessed November 11, 2023. https://www.geowyo.com/absaroka-volcanic-province.html.

Fisher, Mark P., and Ken Steele. “Heart Mountain.” Geology of Wyoming. Accessed April 15, 2024. https://www.geowyo.com/heart-mountain.html.

Hager, M. W. “Fossils of Wyoming Bulletin 54.” Wyoming State Geological Survey, December 1970, 51. https://sales.wsgs.wyo.gov/fossils-of-wyoming-1971/.

Hauge, Thomas A. “The Heart Mountain Detachment, Northwestern Wyoming: 100 Years of Controversy.” In Geology of Wyoming, edited by A. W. Snoke, J. R. Steidtmann, and S. M. Roberts, 530–71. Memoir 5. Geological Survey of Wyoming, 1993. https://sales.wsgs.wyo.gov/geology-of-wyoming-1993/.

Heasler, H. P., C. Jaworowski, R. W. Jones, R. H. De Bruin, and A. J. Ver Ploeg. “A Self-Guided Geologic Tour of the Chief Joseph Scenic Highway and Surrounding Area, Northwestern Wyoming.” Wyoming State Geological Survey Public Information Circular No. 35, 1996, 77. https://sales.wsgs.wyo.gov/a-self-guided-geologic-tour-of-the-chief-joseph-scenic-highway-and-surrounding-area-northwestern-wyoming-1996/.

Hiza, Margaret M. “The Geochemistry and Geochronology of the Eocene Absaroka Volcanic Province Northern Wyoming and Southwest Montana, USA.” Oregon State University, 1999. https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9019s609b.

Johnson, K., and W. Clyde. Ancient Wyoming: A Dozen Lost Worlds Based on the Geology of the Bighorn Basin. Fulcrum Publishing, 2016.

Losh, Steven. “Block Sliding, Heart Mountain Detachment, Wyoming.” Minnesota State University. Accessed March 30, 2024. http://faculty.mnsu.edu/stevenlosh/research/block-sliding-heart-mountain-detachment-wyoming/.

Malone, David H., John P. Craddock, Mark D. Schmitz, Stuart Kenderes, Ben Kraushaar, Caelan J. Murphey, Stefan Nielsen, and Thomas M. Mitchell. “Volcanic Initiation of the Eocene Heart Mountain Slide, Wyoming, USA.” The Journal of Geology 125, no. 4 (July 2017): 439–57. https://doi.org/10.1086/692328.

Mitchell, Thomas M., Steven A. F. Smith, Mark H. Anders, Giulio Di Toro, Stefan Nielsen, Andrea Cavallo, and Andrew D. Beard. “Catastrophic Emplacement of Giant Landslides Aided by Thermal Decomposition: Heart Mountain, Wyoming.” Earth and Planetary Science Letters 411 (2015): 199–207. https://doi.org/10.1016/j.epsl.2014.10.051.

NPS. “Fossils and Paleontology,” July 29, 2022. https://www.nps.gov/subjects/fossils/index.htm.

NPS. “Geologic Time – Major Divisions and NPS Fossils.” Accessed April 16, 2024. https://www.nps.gov/articles/series.htm.

NOAA. “Why Do We Have an Ocean?” National Ocean Service, January 20, 2023. https://oceanservice.noaa.gov/facts/why_oceans.html.

Redfern, R. Origins: The Evolution of Continents, Oceans, and Life. Norman: University of Oklahoma Press, 2001.

Roberts, Laura N Robinson, and Mark A Kirschbaum. “Paleogeography of the Late Cretaceous of the Western Interior of Middle North America-Coal Distribution and Sediment Accumulation.” USGS Professional Paper 1561, 1995, 115. https://pubs.usgs.gov/pp/1561/report.pdf.

Snoke, A. W., J. R. Steidtmann, and S. M. Roberts, eds. Geology of Wyoming. 2 vols. Memoir 5. Geological Survey of Wyoming, 1993. https://sales.wsgs.wyo.gov/geology-of-wyoming-1993/.

USGS, and Annie Carlson. “The Largest Landslide in the World,” November 22, 2021. https://www.usgs.gov/observatories/yvo/news/largest-landslide-world.

Willis, Grant C. “Knowledge of Utah Thrust System Pushes Forward.” Survey Notes 32, no. 1 (January 2000): 1–4. https://ugspub.nr.utah.gov/publications/survey_notes/snt32-1.pdf.

WSGS. “Wyoming’s Fossil Record.” Paleontology. Accessed April 15, 2024. https://www.wsgs.wyo.gov/wyoming-geology/paleontology.aspx.

On the Web

On Wikipedia

Heart Mountain is an 8,123-foot (2,476 m) klippe just north of Cody in the U.S. state of Wyoming, rising from the floor of the Bighorn Basin. The mountain is composed of limestone and dolomite of Ordovician through Mississippian age (about 500 to 350 million years old), but it rests on the Willwood Formation, rocks that are about 55 million years old—rock on the summit of Heart Mountain is thus almost 300 million years older than the rocks at the base. For over one hundred years, geologists have tried to understand how these older rocks came to rest on much younger strata. The carbonate rocks that form Heart Mountain were deposited on a basement of ancient (more than 2.5 billion years old) granite when the area was covered by a large shallow tropical sea. Up until 50 million years ago,…

Classified As

Mountain

Geologic Formations

Willwood Formation (WYTwl;0)

Geologic Formation

Willwood Formation

Geologic Formation