Fossil Butte National Monument was established in 1972 to "preserve for the benefit and enjoyment of future generations outstanding paleontological sites and related geological phenomena and to provide for the display and interpretation of scientific specimens". The Monument is located toward the center of Fossil Basin, 10 miles west of Kemmerer. The butte itself is a major geographic feature of the landscape as you drive west along Highway 30.
52 million years ago the landscape was quite different from today's sagebrush steppe. Fossil Lake, a 1500 square mile freshwater body of water, flourished here in a subtropical environment. Plants and animals very much like those found in South Carolina, Florida and parts of the Gulf Coast were abundant. The evidence for such a different southwest Wyoming from our modern home lies in the many fossils entombed or weathering out of the rocks of Fossil Basin.
At least 27 species of fossil fishes can be found in the sediments of Fossil Lake, none of which belongs exclusively to marine or brackish water groups. Fossils of freshwater plants such as lily pads and cattails are found in the near shore deposits of Fossil Lake. Terrestrial plant fossils such as palms, tree of heaven and poplars are also found in these strata. The remains of mammals, including some of the fossil record's first bats, birds, reptiles, insects, snails and other invertebrates are also found fossilized in the sediments of Fossil Lake.
Fossil Lake was one of three that made up the ancient Green River Lake System. These bodies of water existed for approximately 15 million years. The first, and ultimately largest, of these lakes to appear was Lake Uinta, which eventually straddled eastern Utah and western Colorado. Lake Gosiute followed several million years later, encompassing most of the lower southwestern corner of Wyoming and portions of northeast Utah and northwest Colorado. Fossil Lake deposits closely follow (in geologic time) the first Lake Gosiute deposits. These lakes were connected at times by streams.
The sediments from all three of these lakes are today known as the Green River Formation. The deposits cover some 40,300 square miles with an average thickness of 1,968 feet.
The red and violet badlands of the Wasatch Formation represent the channel and stream deposits that fed the waters of Fossil Lake. A diverse mammal population is represented by the fossils found in these deposits: primitive horses, some of the last primates to be found in North America, extinct browsers, early tapirs, and rodents, as well as carnivores.
Perhaps the first human to find the fossilized remains of this distant world was a Shoshone Indian scrambling along the limestone face of what would one day be called Fossil Butte in search of game or a vantage point from which to observe a herd of bison on the move through Fossil Basin. There is no record of such a discovery, nor are any fossil artifacts present among the arrowheads and potsherds discovered on the monument. Fossils, though, are an element of the culture and history of other Native American nations, so such a discovery may have indeed taken place.
In the 1840s missionaries and explorers such as John C. Fremont documented the discovery of fossil invertebrates in the Green River Formation. In 1856 geologist John Evans made the first recorded discovery of a Green River fish fossil near what is now the town of Green River, Wyoming. He sent his discovery to Joseph Leidy, a professor of anatomy at the University of Pennsylvania who would ultimately come to be known as the "father of American vertebrate paleontology." This fish fossil eventually became known as Knightia, Wyoming's state fossil and the most abundant complete vertebrate fossil found in the world.
As the railroads moved west, excavating enormous amounts of soil and rock, new fossil localities were often uncovered. In the late 1860s, Union Pacific workers uncovered the first major fossil fish beds of the Green River Formation (Lake Gosiute) near Green River. These workers turned a number of these fossils over to Professor Ferdinand Hayden, director of the Geologic and Geographic Survey of the Territories. In 1879 a member of the survey, mineralogist A. C. Peale, was the first to record a description of Fossil Butte itself.
The fossils from Green River were eventually studied and identified by another famous member of that survey, Professor Edward Drinker Cope, who also collected in the Fossil Butte area in the 1870s. He identified a number of hitherto undiscovered specimens. Following his field trips in this area, Professor Cope played a critical role in the "fossil wars" of the late 19th century when he and rival Othneil Charles Marsh directed collecting parties throughout the west in a race for new discoveries. Their competition reached such a frenzy that workers sometimes destroyed or stole each other's fossils, and harassed or spied upon rivals.
Professor Cope had a stalwart ally in Professor Hayden, but Marsh had an even more powerful patron in famed explorer John Wesley Powell. When Powell became the second director of the United States Geological Survey, Cope fell out of favor with the government, and the rest of his life was spent struggling to finance his search for fossils and defending his reputation. His contribution to science, however, is enormous: in addition to the fishes of the Green River Formation, he described over 1,100 North American vertebrate fossils, and his report for the Hayden survey is today popularly known as "Cope's Bible".
Scientists often employed and relied upon professional and amateur collectors in obtaining specimens. Railroad workers would contact eastern institutions when new fossils sites were discovered. These men would often find rewarding second jobs moonlighting as fossil collectors for Professors Cope or Marsh or some other researcher.
The explorers would hire teams of local men, sometimes with less than satisfying results. Cope writes of one teamster who in the process of tracking down some stray mules managed to find a saloon, drank himself into a stupor, let the mules starve, then stole provisions in anticipation of his being fired. Many collectors, however, were extraordinarily loyal and capable workers who spent numerous field seasons in the employ of the scientists from the east.
Since the publication of "Cope's Bible" in 1884, few scientific papers were presented on the fossil fishes of Fossil Basin and the greater Green River Formation until after World War II. From the 1920s to the 1960s Dr. Wilmot Bradley, a geologist with the U. S. Geological Survey, produced a considerable amount of information on the geology of the Green River Formation. In one of these publications he described the “beautifully preserved fish, with delicate fins, tail rays and scales, all virtually undisturbed, are entombed here in thinly levered sediments recording the abundant life and ecology of an ancient subtropical lake."
In the 1920s and 1930s, Dr. R. W. Brown, also of the U. S. Geological Survey, extensively described the plant life of the Green River Formation. In the 1950s and 60s Dr. Lewis Gazin of the Smithsonian studied the mammalian faunas of southwestern Wyoming, and noted individual animals from the Green River and Wasatch formations, such as primates and early horses. Although found in Fossil Basin in the early 1930s, the early bat, Icaronycteris index, was not described until 1966 by Dr. Glenn L. Jepsen of Princeton University. Dr. Paul O. McGrew, of the University of Wyoming conducted substantial research in Fossil Basin throughout the 60s and 70s. He co-wrote (with Dr. Michael Casilliano, also of UW) "The Geologic History of Fossil Butte National Monument and Fossil Basin". Dr. McGrew also provided considerable scientific input to the developers of Fossil Butte National Monument.
Scientific research in the larger Green River Formation as well as the smaller area of Fossil Basin continues today. Since its inception, Fossil Butte National Monument has supported this research in a variety of ways: from National Park Service financial assistance, scientific support from the park paleontologist, logistical support from monument staff, as well as functioning as an informal base of operations. Through such efforts, researchers are better able to interpret this remarkable resource for not only other scientists, but for the thousands of persons from around the world who visit Fossil Butte National Monument annually.
Visit www.nps.gov/fobu for more information.