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Explorer Corps Marker: Millard County

Find the Marker

The Millard County marker is just outside of the entrance to the R.J. Law Community Center at 75 W. Main St in Delta. The marker highlights trilobites, ancient marine arthropods frequently found in the Wheeler Formation in the House Range, about one hour west of Delta.

GPS 39°21’7.38”N 112°34’35.3784”W

Dig Deeper

At a glance, trilobites might seem like unassuming little fossils. The bug-eyed arthropods are often small enough to fit comfortably in the palm of a child’s hand, reminders of a time long before bones or the dinosaurs that grace so many museum halls. But don’t underestimate these ancient invertebrates. They are part of one of the most spectacular records of Cambrian life anywhere on the planet.

The Cambrian Period, between 541-485 million years ago, was when animal life proliferated through ancient seas. This was the time of the earliest arthropods, mollusks, and even vertebrate ancestors, not to mention creatures so strange that they might seem to defy classification. The Burgess Shale of western Canada is perhaps the most famous location where such fossils are found, but, NHMU museum and paleontology curator Randall Irmis points out, the Cambrian record in Utah offers the Burgess Shale some solid competition. “The House Range in Millard County preserves perhaps the best record of ancient life from the Cambrian Period anywhere in the world,” he notes.

Paleontologists have been searching this area for a long time. The first descriptions of fossils from the House Range date back to the 1850s. Trilobites were a big draw to this area. Multiple species have been found in these rocks, but the most numerous is one called Elrathia kingi. “This trilobite really should be Utah’s state fossil,” Irmis says, because millions of Elrathia kingi have been uncovered here. If you see a trilobite in a rock shop or in an educational fossil set, chances are it's an Elrathia kingi from western Utah.

But trilobites are only part of the story. The House Range doesn’t represent just one slice of time, but at least three. The Wheeler, Marjum, and Weeks formations have all yielded Cambrian fossils that are separated by hundreds of thousands – even millions – of years. And while hard-bodied fossils are the most common, these rocks also contain the rare and delicate remains of soft-bodied animals. “Many layers preserve soft-bodied animals and soft tissues of animals with hard parts,” Irmis says, from worms to strange, spaceship-like invertebrates with shutter-shaped mouths, grasping appendages, and compound eyes called anomalocaridids.

“There are a few other places in Utah and the Intermountain West that have important Cambrian fossils,” Irmis says, “but none have anywhere near the quantity of fossils, diversity of species, quality of preservation, and range of geologic ages that are found in the House Range.” In fact, in 2021 the NHMU accepted a collection of these unique fossils from the Bureau of Land Management that includes species that have never been seen before. Even though experts have been combing these rocks for more than two centuries, paleontologists have really only just begun to recognize, categorize, and understand the sheer diversity of life that thrived in Cambrian seas that covered ancient Utah. “Some of the species found in these deposits are so weird that it’s hard for paleontologists to figure out which group they’re related to,” Irmis says, adding even more mystery to some of Utah’s oldest fossils.

Want to Go Farther?

While hiking in the House Range, you very well could come across a 500 million-year-old trilobite if you keep your eyes peeled!

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