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Green River Formation

One of the most important fossil sites for understanding the Eocene is found at Green River, located in western Colorado, eastern Utah and southwestern Wyoming in the United States. During the Eocene, this region was located at much the same latitude it is today, though global climate was more equable. Therefore, the climate in which the organisms lived differs somewhat from that of the present-day western United States.

The fossils, especially plants, found at this site indicate that the climate was moist temperate or sub-tropical, with temperatures ranging from 15 to 20 degrees Celsius. In addition to the plants, another piece of evidence suggesting that the climate was sub-tropical was the presence of fossilized crocodiles. Crocodiles can only survive in areas with a constant, warm temperature.

If you were able to visit the Green River locality during the Eocene, you would see palms, cat-tails, sycamores, and other familiar plants from North America, but you would also see some that are today more common in, or restricted to, eastern Asia. A series of large inland lakes extended across the region, and it is in the bottoms of these lakes that various plants and animals were buried and fossilized. These lakes later dried up as the local climate changed, and many of the plants and animals living here went extinct.

The data concerning the depth and chemical makeup of the lakes is so far inconclusive, because there are no definite independent environmental indicators in the micrite beds, which are beds of very fine (1-5 microns) carbonate crystals (either calcite or aragonite). Micrite can precipitate from seawater or form from the breakdown of larger carbonate grains. There are two hypotheses concerning the depth and conditions of the lakes. The first is that the lake was deep and stratified (Bradley, 1948), the second is that the lakes were unstratified, and had varying depths and salt concentrations (Buchheim and Surdham, 1981).

The sedimentary composition of the Green River locality includes many layers. The major sedimentary types are primarily oolitic grindstones (grains consisting of multiple coatings of carbonate, usually calcite and/or aragonite, that precipitated on a nucleus; they are round and smooth, and form in shallow water depostitional environments), packstones (porous sedimentary rocks), oil shale (fine-grained sedimentary rocks composed of particles consisting of silica-containing minerals) and mudstones.

The occurrence of these different sediments varies depending on the depth from the surface. The fossil distribution also varies with the depth. For example, the deepest layer of the sediment studied does not contain any fish fossils. These fossils were found during commercial fishing expeditions, and can now be found in private museums and collections. The museums include the Museum of Western Colorado, and over 15,000 are housed at the US National Museum of Natural History (Smithsonian). The plant type materials are housed here at UCMP.

Scientists dated the material in the Green River Locality using several approaches. For example, to determine when the transition from the Wasatchian-Bridgerian (early to middle Eocene), in which a significant change occurred in the fauna of Western North America, scientists used Chron C22r methods, which are stratigraphic methods of dating. They concluded that the transition occurred between 49.7 and 50.7 million years ago and lasted less than half a million years (Clyde, W.C. et al, 1995). To determine the depths at which these fossils occur, scientists compared the fossils at each level to known species of each period. Other methods to date fossils and rocks include radiometric dating and paleomagnetism, a method in which magnetic polarization, acquired by the minerals in a rock at the time the rock was deposited or solidified, is analyzed.

Approximately 60 vertebrate taxa have been found at Green River, including fish, reptiles, birds and mammals. Eleven species of reptiles have been found, including one species of snake, Boavus idelmani. Invertebrate fossils are abundant, with remnants of snails and insects being common. The plant fossils, including many reeds, leaves and wood specimens, are also very prevalent at Green River. A large majority of known fossils are fragmentary but some complete skeletons exist of fish, birds, reptiles and one mammal, Brachianodon westorum.

There are many reasons that explain why the fossils are found in fragments. These include scavenging, fossil disturbance, lake currents, decomposition of the body prior to fossilization and changing physical conditions. A specific example is the process of fossilization for fish in the Green River lakes. These fossils range from total disarticulation, such as scattered bones and gar scales, to complete skeletons. Fossils containing scattered bones are attributed to the decaying process that usually occurs after a fish dies. In addition, temperature affects whether or not a fish will sink or float, by altering the volume of gas within the swim bladder.

The fish’s unregulated swim bladder causes the fish to float on the surface of the water. As the fish decays, currents move the fish along the lake surface until it is caught in vegetation, causing bones to drop from the skeleton in a well-ordered sequence. These bones sink to the lakebed and are preserved. Of fishes that have sunk to the lake floor, scavengers, feeding on the top surface of the decaying fish, cause the dispersal of bones to be less orderly, and breakage of bone. Because of these decaying and dispersal processes, the fossilized fish are rarely found at the same location where they died.

Due to the fact that dead fish usually float, it is unusual to find an intact skeleton fossilized at the lake’s floor. Furthermore, it is also unusual for scavengers not to have disturbed the carcass. Because complete remains have been found at Green River, we can infer several things about the conditions where these fish died. First, the temperature must have been low at the time of death, to prevent the swim bladder from inflating completely. However, as stated before, the temperature at this site is usually considered subtropical and constant. This preservation of the fish implies that the climate did indeed vary at some point during the Eocene.

This suggestion is supported by Grande’s hypothesis that the lakes were characterized by a complicated history in which the shapes and volumes of the lakes were changed due to tectonics, sedimentary depositions, and changes in both drainage and climate (Grande, 1980). Secondly, the depth of the lake must have been great, allowing for little oxygen at the greatest depth. This would prevent scavengers from surviving the anoxic conditions, and disturbing the fish (Elder, 1985).

The Green River Formation is the site at which the fossil of the oldest known flying mammal was found. This organism, a bat, Icaronycteris index, was preserved with its skeleton, membranes and cartilage intact. It was discovered along with food still inside its body and waste not yet disposed, so some of the flora, algae, pollen and arthropods of the time can be studied. It is rare that a complete fossil is found, and this makes the bat fossil very useful for paleontologists to study.

The bat was found in a position that is common for dead bats; its wings were folded and the femora were at a specific angle to the vertebral column. It is unclear, however, how the bat died; lightning or hail are the most likely guesses. From the sediment and flora found with the bat, paleontologists can draw conclusions about the depth of Fossil Lake, and the temperature. Jepsen (1966) suggests that it was about 2200 meters above sea level. Another interesting question that the fossilized bat might help scientists determine is at what point in evolutionary history did echolocation appear.

The Green River site is important because it reveals information about the climate during the Eocene and the transitions during the period itself, including the significant faunal change that occurred in North America. The site reveals much information because so many of the fossils were found intact. The placement and orientation of these fossils also tells researchers about the conditions at Green River during the Eocene. In Europe and Asia, Eocene fossil localities are incomplete or have been disturbed, so the fact that the Green River locality is so complete allows scientists to form a more comprehensive picture of the era. The bat fossil can tell researchers about the evolutionary history of echolocation and the evolution of life in the early Tertiary.

Wheeler Shale – Delta, Utah

The Wheeler Shale, close to Delta, Utah; was named by famous paleontologist Charles Walcott. The area is a 500 Million year old (Cambrian) fossil locality that is world famous for producing prolific amounts of fossils. The more common to be found are agnostides and Elrathia kingii trilobite remains. Other soft bodied organisms are locally preserved, Including some plant and stromatalite fossils. The preservation style of the wheeler shale (carbonaceous film) is normally associated with the more famous Burgess Shale. As such, the Wheeler Shale also represents a Konservat-Lagerstätten.

Together with the Marjum Formation and lower Weeks Formation, the Wheeler Shale forms 1,600 to 2,000 ft. of limestone and shale exposed in one of the thickest, most fossiliferous, and best exposed sequences of Middle Cambrian rocks in North America. With a locality near the Wheeler Amphitheater, House Range, Millard County, in western Utah. The Wheeler Shale consists primarily of highly calcareous shale, shaley limestone, mudstone and thin, flaggy limestone. The Wheeler Formation extends into the Drum Range, northwest of the House Range where similar fossils and preservation are found.

Solnhofen, Germany

The Solnhofen Limestone ranks as one of the most most famous Lagerstatte in the world. This fossil site in the state of Bavaria in Germany has yielded an amazing diversity of fossil organisms, often deposits known for the exceptional preservation of fossilized organisms, where the soft parts are often preserved (a Konservat-Lagerstätte), provides a snapshot of Jurassic life 155 million years ago. The most famous are the eight fossils of the first bird known in detail, Archaeopteryx. The first Archaeopteryx fossil was discovered in 1860, a single feather. The next year a very complete example was found and sold to the British Museum.

The next specimen was discovered sixteen years later, and is known as the Berlin specimen. It is considered by some to be the most valuable fossil in the world today. With its combination of characteristics of reptile-like teeth and tail with the feathers of a bird, it was a quintessential missing link that supporters of Charles Darwin could refer to as proof of the theory of evolution. In the subsequent 140 plus years since the first bird was found, only six more have been added to the handfull of examples.

The discovery of the wonderful fossils of Solnhofen may be attributed to the longtime uses to which the “plattenkalk” has been used. This is a German word that seems more appropriate than the English “platy limestone”. Plattenkalk was used as early as the Stone Age for making drawings and colored murals due to its softness. The flat, regularly shaped material was suitable for paving roads and building walls, something done by the ancient Romans who for a time held sway over the region. In the Middle Ages, the stone was used as floor and roofing material.

The mosaic floor of the church of Hagia Sofia in Istanbul was made of limestone from the region. Artisans also used the material in the making of bas-relief sculptures and headstones. A decisive turning point in the history of the area was the discovery in 1673 by Alois Senefelder that the fine-grained material could be employed in lithography, a use that caused quarrying to skyrocket. Although the heyday of lithography only lasted a hundred years or so, it was the single most important impetus in the discovery of fossils.

The fossils have always been prized by local residents because of their beauty. As those most intimately associated with the limestone, the quarrymen were obviously those who were responsible for their discovery. At first, quarry owners allowed the workers to keep the fossils they found, but as interest in them (and consequently, value) grew, this practice stopped. The variety and number of fossils known is deceptive. The occurrence of fossils is quite low. Indeed, a worker can quarry for an entire day and find not a single one. The hundreds of years of quarrying are what make them seem so apparently common.

The sheets of limestone are so regular that we can only conclude that they were deposited in a calm environment. The deposits were evidently laid down under a stable body of water that had some connection to the Tethys Sea. Sponges and corals grew on rises in this sea, forming lagoons. In fact, remnants of a coral reef can be found in the area to the south of Solnhofen.

The region must have been near land, however, due to the discovery of insects such as wonderfully-preserved dragonflies. Assuming that Jurassic coral reefs grew in modes similar to those of today, the surface of the reefs would have been only 10 meters or so under water. The maximum depth has been estimated by some to have been 60 meters (200 feet).

These isolated lagoons would have been quite stagnant due to little exchange of water with the sea. Anoxic conditions would have been ideal for preventing destruction of organisms that found their way into the lagoons. Some evidently survived for short periods. One of the most famous examples of this are the horseshoe crab “death spirals’ that exist in which a spiral trackway has been preserved with the defunct arthropod in the center, presumably preserving its last efforts at survival.

The theory most often proposed for the toxicity of the waters has been that of hypersalinity, the excessive concentration of salt. If the area were hot and dry, with little runoff from the land to the north, conditions would have been ideal for promoting excessive evaporation of water with concomitant increase in the salinity in the lagoons. The dense brine would collect in the bottom of the pools, excluding most life, as sensitivity to even minute changes in density has been seen in many marine organisms. Once an organism had been washed into the lagoon by the action of a storm, it would quickly succumb to the toxic conditions that existed within. The hypersaline, anoxic floor was ideal for the preservation of the body, often even leaving evidence of soft tissues.

Storms would have often brought in a suspension of finely-dispersed lime. Such storms would have brought in the amazing diversity of life we know from the region: pterosaurs, dinosaurs like Compsognathus and Archaeopteryx, dragonflies, and other insects, fish, turtles, crinoids, starfish, jellyfish, ammonites, worms, plants, and many, many more. The number of species found exceeds 500. The limestone deposits of Solnhofen open a door closed to us over 150 million years ago, affording us a look at a wonderful diversity of life from both the land and the sea of the Jurassic.

Badlands, South Dakota

Badlands is a term used to denote what are usually areas that are extensively eroded by wind and water, with many canyons, ravines, and gullies, and other complex geological formations. The term can be taken to mean, “bad lands to cross”. Such lands are commonly the source of rich fossil beds because erosion may rapidly expose fossil bearing sedimentary layers and the fossils that are contained.

Numerous fossil bearing badland formations exist in the United States and Canada. These include Badlands National Park in South Dakota, Makoshika State Park in Montana, Theodore Roosevelt National Park in North Dakota; Toadstool Geologic Park in the Oglala National Grassland of northwestern Nebraska; Dinosaur Provincial Park is and the Royal Tyrrell Museum of Paleontology in Alberta, Canada. The Dinosaur National Monument in Utah is another famous badlands areas.

The Badlands of South Dakota, also simply called the Badlands, or the White River Badlands, or the White River Group, is an extensive area within parts of Colorado, Wyoming, Nebraska, in addition to South Dakota. This vast area is famous for its diverse and well preserved mammal fossils that date from the late Eocene to early Oligocene.

Throughout the late 1800s and continuing today, scientists and institutions from all over the world have benefited from the fossil resources of the White River Badlands. The White River Badlands are internationally famous for having the richest deposits of Oligocene mammals known.

The faunal list is huge, and includes rhinoceroses, Hyracodon, Subhyracodon, and Metamynodon; the Tapiroids Colodon and Protapirus; Horses such as Mesohippus and Miohippus; pig relatives with large heads such as Archaeotherium; Horned deer-like Protoceras; the hyaena-toothed carnivore Hyaenodon; the hippopotamus ancestors Aepinacodon and Heptacodon; dog ancestor Hesperocyon; the camel-like Poebrotherium.

The area is especially noted for Oreodonts, which scientists believe were distantly related to pigs, hogs, camels, hippopotamuses, and the pig-like peccaries. Of particular interest are the Nimravid cats, sometimes called “False sabre-tooths”, are an extinct family of mammalian carnivores that existed at the top of the food chain. Although some Nimravids morphologically resembled the sabre-toothed cats of genus Smilodon, they were not closely related. Rather, they are believed to have evolved a similar form through the process of parallel evolution. Genera include Hoplophoneus, Eusmilus, Dinictis, and Nimravus.

The Brule Formation is the uppermost formation in the White River Group. This important fossil formation was named for the Brule Indians that lived in western Nebraska and South Dakota. The Brule Formation is exposed over a vast area of the West, including Nebraska, North and South Dakota, Wyoming, and Colorado, and yields abundant fossils as layers are eroded. Toadstool Geologic Park is located in the Oglala National Grassland in far northwestern Nebraska.

Its stratigraphy begins with the oldest Eocene-age Chadron Formation, followed by the Oligocene Brule Formation, and finally the Miocene age rocks of the Arikaree Group. Ichnofossils (trackways) are especially abundant in the Brule Formation, giving scientists insight into the behavior of the Oligocene mammals.

La Brea Tar Pits, California

As far as parks go, people rarely ever describe them as unusual. When you think of parks, the first thing that would come to your mind would most likely be lush green surroundings with cute woodland creatures instead of bubbling asphalt pits and all sorts of fossils. A trip to Hancock Park, located in the Miracle Mile district of Los Angeles, are the La Brea Tar Pits, one of the most popular and unusual tourist attractions in the city, might change your perception about parks.

Located in the heart of urban Los Angeles is a cluster of tar pits, famous all over the world for being one of the richest sources of fossils dating back to the Ice Age. The tar pits are a result of continuous oil seepage, spanning for thousands of years, between the areas now known as Hancock Park and Salt Lake Oil Field. Occasionally, certain animals would wander off into the area where these pools formed and be trapped in the tar pits. Predators lured by a trapped prey would find themselves sharing the same fate.

Aside from the fossils of huge mammals like mammoths, saber-toothed cats, and dire wolves, scientists have also uncovered “microfossils” like insects, plant remnants, including dust and pollen grain perfectly preserved in the pit’s asphalts. The oldest material obtained from the La Brea pits is approximated to be around 40,000 years old.

Visitors can walk around and observe the various small pits scattered throughout the area. You can see how the fossils originally looked like upon discovery in the Observation Pit and even see an actual excavation when you come across Pit 91. Lake Pit, which is the largest pit, features a reenactment of how animals get trapped in the tar pits using life-size models of Columbian Mammoths.


Jurrasic Coast, England

Jurassic Coast and the Lyme Regis of England

The Jurassic Coast is one of the most spectacular coastlines in England, and has recently been given World Heritage status in recognition of its geological importance. The coast extends for 95 miles and takes in dramatic cliffs, spectacular arches and sea stacks. This coastal scenery takes visitors on a 185 million year old journey. As the visitor moves along the coast from Exmouth to Stobden Bay, the dramatic story of the earth’s formation unfolds. This is the finest record of the Triassic, Jurassic and Cretaceous periods in the world. East Devon is the oldest part of the Jurassic Coast, dating back to the Triassic period. Visitors to the whole area can enjoy fossil hunting in many of the beach locations.
Charmouth is one of the most famous Jurassic locations, renowned for its cliffs which are rich in fossils. The cliffs are especially popular with fossil hunters. Fossils are largely found on the foreshore and at the base of scree slopes and slippages. Most of the fossils are sea creatures and shellfish which date from a period when the coast was surrounded by a warm tropical sea. However, fossil detectives should check tide times and take care as the sea can cut off some locations.

One of the most notable fossil hunters of all time happened to be from Lyme Regis. Her name was Mary Anning. Mary Anning first became interested in fossils when she accompanied her father on amateur expeditions at the cliffs of Lyme Regis, a treasure trove of remnants from the Jurassic period, near her childhood home in southern England. They sold shells and fossils to tourists and collectors to help make ends meet, and despite a lack of any formal education she taught herself the geology and anatomy needed to became a respected paleontologist. Among her discoveries were the earliest known long-necked Plesiosaur (commonly called the “sea-dragon”), the first English specimen of Ichthyosaurus (“fish-lizard” or “crocodile”), a Pterodactylus (“flying-dragon”), and the Squaloraja (a ray/shark). She assembled skeletal remains of these and other extinct animals, classified the belemnites and ammonites, reptiles and fishes, and made technically proficient drawings of their bone structure. She also discovered that squid-like belemnites could be ground up to be used as ink, and she was one of her era’s preeminent experts on coprolites (fossilized feces).

Her work was often condemned as blasphemous, since the reassembled fossils’ existence was at odds with Biblical stories and the commonly accepted timeline extrapolated from the Bible. She was said to have had a long affair with geologist Henry de la Beche, but this may have been a rumor that began because he was among the first scientists to take her work seriously. In addition to frequent meetings with de la Beche, she corresponded with William Buckland and Gideon Mantell. She never taught, and for most of her life her income came primarily from selling unimportant but visually interesting fossils at a souvenir stand on the beach near her home. According to England’s Natural History Museum, the tongue-twister “She sells seashells by the sea shore” was inspired by the increasingly famous Anning. In 1838 she was awarded an annual stipend from the British Association for the Advancement of Science, augmented eight years later by a second stipend from the Geological Society of London, though on account of her gender she was unable to join either group. In 1847, as she was dying of breast cancer, she was named an honorary member of the Geological Society.

Petrified Forest, Arizona

With a total of 93,533 acres, this Eastern Arizona gem was proclaimed a national monument in 1906, then designated a national park in 1962. As part of the Painted Desert, it contains the largest known display of petrified wood in the world. There are six separate “forests,” each with great logs of jasper and agate lying on the ground surrounded by the varied colors of endless fragments and small chips. Dating to about 230 million years ago or the Triassic period, these “stone trees” were killed by natural processes, such as fire, insect attacks, and fungus (or rot).

The trees were deeply buried in mud and sand that contained silica-rich volcanic ash. The logs became petrified as the minerals, carried into the wood by groundwater, replaced the wood cells. As the surrounding material was eroded away, the petrified trees were exposed on the surface. Prehistoric Native Americans also lived amongst the stone trees. The ruins of their dwellings and their petroglyphs (ancient rock art) remain. The first known report of the petrified forests was made by Lt. Lorenzo Sitgreaves, an army officer who explored the area in 1851, and the forests were virtually unknown until the late 1870s.

Burgess Shale, Canada

The Burgess Shale is a very famous fossil formation named after the nearby Burgess Pass. This site is high in the Canadian Rockies within Yoho National Park near the town of Field, British Columbia, Canada. The Burgess Shale was discovered in 1909 by famed paleontologist Charles Doolittle Walcott, who returned time and again to extensively study its fossils. Walcott described a large diversity of previously unknown arthropods, and most importantly many forms of previously unknown phyla as well as many forms that remain enigmatic today.

The fossils were particularly important at the time to understand Cambrian paleobiology because of their often exquisite preservation that included soft body parts. Many such Cambrian sites have since been discovered, most notably the Chengjiang Maotianshan Shales, which are collectively called sites with Burgess Shale-like preservation.

The Burgess Shale fossils are about 505 million years old, some 20 million years younger than those from Chengjiang. In fact, the Burgess Shale and Chengjiang have considerable overlap in faunal forms. Less well known is that Cambrian formations in the House Range of Utah yield many fossils like the Burgess Shale, though the soft tissue preservation is usually not as good.

The Burgess Shale Formation comprises 10 separate members, the most famous being the Walcott Quarry Shale Member comprising the greater phyllopod bed. The Burgess Shale comprises shale, limestone and siltstone and extends in a large area in outcrops of the Stephen Formation that exhibite different faunal mixes. The fossils of the Burgess Shale are preserved as black carbon films on black shales. Scientists long believed the deposits were formed when areas of muddy ocean floor slid into a lower place creating an anoxic (oxygen-starved) environment that was particularly favorable to fossilization because decay was inhibited. More recent research that oxygen was continually present in the sediment

While there are older Cambrian formations, the Burgess Shale was science’s first glimpse of the Cambrian Explosion in the fossil record. The extensive diverse fauna generally new to science and their often exquisite soft-bodied preservation caused Walcott to return repeatedly to the fossil site until 1924. By age 74 he had amassed more than 65,000 specimens. Describing the fossils was a vast task the Walcott continued until his death in 1927. Walcott, influenced by the opinion of scientific peers, tried to associate the fossils with living taxa, which delayed the scientific significant of them to be delayed by serveral decades. Three decades of study commencing in the 1960′s led to the Burgess Shale ultimately attaining the recognition of today as a remarkable rock record of early Cambrian life and its early diversification.

Hell creek Formation, Montana

The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation spans about 1.3 million years, terminating at the Cretaceous–Paleogene boundary, dated to 65.5 million years ago.

The Hell Creek Formation occurs in Montana and portions of North Dakota, South Dakota, and Wyoming. In Montana, the Hell Creek Formation overlies the Fox Hills Formation and is the uppermost formation of the Cretaceous period. “Pompey’s Pillar” at the Pompeys Pillar National Monument is a small isolated section of the Hell Creek Formation.

It is a series of fresh and brackish-water clays, mudstones, and sandstones deposited during the Maastrichtian, the last part of the Cretaceous period, by fluvial activity in fluctuating river channels and deltas and very occasional peaty swamp deposits along the low-lying eastern continental margin fronting the late Cretaceous Western Interior Seaway. The climate was mild, and the presence of crocodilians suggests a sub-tropical climate, with no prolonged annual cold. The famous iridium-enriched Cretaceous–Paleogene boundary, which separates the Cretaceous from the Cenozoic, occurs as a discontinuous but distinct thin marker bedding within the Formation, near its uppermost strata.

The world’s largest collection of Hell Creek fossils is housed and exhibited at the Museum of the Rockies, in Bozeman, Montana. The specimens displayed are the result of the museum’s Hell Creek Project, a joint effort between the museum, Montana State University, the University of California, Berkeley, the University of North Dakota and the University of North Carolina which began in 1998. The formation is also a popular location for commercial excavations.

Dinosaur Monument, Utah

For a long stretch of the early 20th century, the area now known as Dinosaur National Monument was the near-exclusive hunting ground of Pittsburgh’s Carnegie Museum of Natural History. The site was discovered in 1909 by a Carnegie paleontologist, and over the next dozen years, hundreds of tons of fossils were shipped back east, including near-intact specimens of Allosaurus, Apatosaurus, and Stegosaurus. In fact, part of the reason President Woodrow Wilson turned this isolated stretch of land into a national monument in 1915 is that Carnegie was trying to buy the territory, which would have resulted in its having a fossil monopoly.
Dinosaur National Monument is most famous for its slice of the Morrison Formation, a huge expanse of late Jurassic-period rock that covers 1.5 million square miles of the North American continent. It’s believed that the Utah portion of the Morrison Formation was once a low-lying floodplain crisscrossed by various rivers; periodic floods drowned the dinosaur population, and their bones were well-preserved in the silt for the next 150 million years.

Unfortunately, the Quarry Visitor Center of Dinosaur National Monument has been closed for the last few years, in part because the same geologic formation that preserves dinosaurs so well has proven to be an unstable foundation for this large (and popular) building! However, some fossils can still be seen by taking the half-mile hike from the temporary visitor center, as the main installation undergoes repairs.