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Map of region around Utah 515 million years ago during the Middle Cambrian showing Millard County in green. Sevier (Playa) Lake is in blue and outcropping Cambrian strata in black. ~C N indicates approximate position of North relative to Utah during the Cambrian. Paleogeographic basemap by Ron Blakey (Colorado Plateau Geosystems). Cambrian outcrop after Hintze and Davis (2003; 17 MB PDF).
Utah Geological Survey
Cambrian Fossils in Utah's West Desert, Millard County
Utah is recognized for having the longest and most diverse dinosaur record in the nation. Yet, the Cambrian rocks in Utah's West Desert contain one of our nation's best records of the early evolution of life on Earth. View a slideshow of rocks and fossils from the West Desert here. During the Cambrian Period, North America straddled the Equator and the continent was oriented nearly 90 degrees clockwise of its present position. The Cambrian coastline extended north-south across Utah shifting southward (our east) with rising sea level. This resulted in a nearly complete sequence of Cambrian rocks preserved in Utah's West Desert on what was the northern coastline of early North America. When Tertiary extension forces formed the Basin and Range Geological Province throughout the last 20 million years, these Cambrian rocks became well-exposed across western and central Utah, revealing the extraordinary fossil record within. Nowhere is this geology better exposed than in Millard County, Utah. Refer to Hintze and Davis (2003) (17 MB PDF) for a detailed discussion of the county's geology. The Cambrian is best known for the "Cambrian Explosion" (or "Cambrian Radiation") , when a great diversity of multicellular animals first appears. The first scientific report on these fossils was a description of Elrathia kingii in 1860, probably the world's most well-known trilobite species.
These rocks are renowned for their diverse trilobite faunas. The Wheeler Shale yields many specimens whose shells have been "thickened" by secondary calcite, such that the fossils literally pop out of the rock. Specimens have been found that were drilled by Native Americans for jewelry. Most fossils from these rocks are much more delicate and must be preserved on the rock in which they were found. In many cases a thin layer of rock will cover the fossil and it much be carefully cleaned with a fine, hard needle under a magnifying lens.
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Trilobites and rare brachiopods preserved on thin limestone bed, upper Weeks Formation in North Canyon, House Range. The fauna, likely buried during a storm event, mostly consists of Norwoodia boninoi, with fewer Menomenia sahratiani, Coosella kieri, Triadaspis bigeneris, Genevievella sp., and unidentified agnostoid trilobites and inarticulated brachiopods. Photo by Carlo Kier from Robison and Babcock (2011) courtesy of Dick Robison.
If you are willing to pay for the opportunity to collect trilobites, The U-Dig Fossils quarry in the Wheeler Amphitheater leased on Utah state land is a sure bet. However, Utah's public lands are open to collecting with hand tools. Reasonable numbers of invertebrate fossils can be collected for personal use. Just remember to leave any sites you investigate exactly the way you found them. Use the resources here to identify your finds.
A great number of the significant discoveries came to the attention of scientists through the collecting efforts of three (now four) generations of Utah's own Lloyd Gunther family. The importance of their discoveries and their long association with scientists interested in these rocks resulted in their receiving the first Harrell L. Strimple Award by the Paleontological Society in 1984 for outstanding achievement in paleontology by amateurs. The Lloyd and Val Gunther's lengthy 1981 article "Some Middle Cambrian Fossil from Utah" (9.5 MB PDF) is the first place most people go to identify their discoveries.
It is important to note that new species are found in Utah's West Desert all the time, with dozens of new trilobite species illustrated in Robison and Babcock's recent (2011) online publication "Systematics, paleobiology, and taphonomy of some exceptionally preserved trilobites from Cambrian Lagerstätten of Utah."
In addition to trilobites, the Cambrian rocks preserve a wealth of other animals. Perhaps most excitingly, soft bodied fossils are preserved throughout the Middle Cambrian starting with the Spence Shale in the Wellsville Mountains in northern Utah and in ascending order the Wheeler, Marjum/Pierson Cove, and Weeks Formations in Utah's West Desert. In both Canada with the Burgess Shale and China with the Chengjiang fauna, the protection of these sites is comparable to that of our own U.S. National Parks. Ongoing funded excavations are a major part of the management of these sites. This extraordinary fauna includes nearly all of the taxonomic groups found in the Burgess Shale and even goes so far as to preserve the most delicate of fossils, jellyfish.
Know Before You Go
If you come to Utah to collect fossils in Utah's West Desert make sure your car is full of gas and that you are carrying plenty of water. Tell someone, where you are going and make arrangements to check in with someone to tell them you're OK after your done; as this is rugged remote country that is subject to fiercely hot days and cold nights. Before heading into the back country stop in the Bureau of Land Management's district office in Fillmore, Utah and pick up copies of the 1:100,000 scale "Surface Management Maps" for the areas you intend to explore as it is important to know "whose" land you are collecting on. These maps show surface ownership and tend to be more reliable that GPS navigation units in regard to roads. Ask if there have been any changes in the collecting rules for common invertebrate fossils on federal lands, noting that, while state lands may be a bit more relaxed in their collecting rules, they largely follow the lead of the federal government. To insure the educational and scientific value of your fossils, take notes about your expedition, directions to the sites you discover, sketch pictures of the outcrops, note the kind and character of the rocks you find your fossils in using the references Hintzi and Davis's (2003) book (17 MB PDF) on the geology of Millard County and the four published online 1:100,000 Geological Maps covering Millard County (Delta, Tule Valley, Wah Wah Mountains North, and Richfield) to help you place your fossils into stratigraphic context. Knowing which rock layer (formation) your fossils are from gives you a much closer estimate as to how old your fossils are. Use a GPS unit to precisely record where your fossils are from using the navigation datum NAD-83 so that your fossil sites can be precisely located on your map. Finally, take pictures and not just up close at the site, but also from a distance so the site can be noted from the road or as you hike up a canyon to it.
Keep in mind that soft bodied fossils from the Cambrian are exceedingly rare and new fossils of all kinds are being discovered all the time. By taking careful notes and working with scientists and museums, you might find the next new fossil species discovered in Utah's West Desert is named after you.
Article and photographs provided by James I. Kirkland (State Paleontologist, Utah Geological Survey)
Additional important websites for identifying fossils from Utah West Desert
2013 Paleozoic Partner feature articles: | January: Fossils of the 2013 National Fossil Day Artwork | February: Paleontological Research Institution, Museum of the Earth | March: Falls of the Ohio State Park | April: Field Museum of Natural History, Mazon Creek Collection | May: Prehistoric Trackways National Monument | June: Cincinnati Museum Center | July: Glacier Bay National Park & Preserve | August: University of Michican Museum of Paleontology, Silica Formation Fossils | September: Yale Peabody Museum of Natural History, Beecher's Trilobite Bed | October: Guadalupe Mountains National Park | November: Utah Geological Survey, Millard County Cambrian Fossils | December: Denver Museum of Nature and Science, High-Altitude Mass Extinction |