Smithsonian.com

Tracks made by a medium-sized theropod on a slab of rock just outside of Moab, Utah. Photo by author.

Two years ago, I visited the American West for the first time. I was immediately hooked. Seeing the morning sunlight hit the dinosaur-rich Jurassic rock of northern Utah’s Dinosaur National Monument was what really did it for me. When I saw that, I knew that I had to move out West, and a few weeks ago I settled in Salt Lake City to devote myself to writing about the prehistoric past. I now live right in the middle of dinosaur country—some of North America’s most productive and important dinosaur sites are within a day’s drive—and this past weekend I had the chance to visit a few located just a few hours from my new hometown.

At the southern tip of the series of highways making up the Dinosaur Diamond, Moab is right in the middle of dinosaur country. The geologic strata of the area is piled high with sedimentary rock from the heyday of the dinosaurs—from the Late Triassic through the Early Cretaceous in many places—and, at a few spots, vestiges left by dinosaurs can be easily seen. One such place is right along Potash Road, just outside Moab itself.

Left in Navajo Sandstone dating to about 190 million years ago, the Potash Road dinosaur tracks come from a time tens of millions of years before the famous Jurassic fauna of the Morrison Formation. The world was quite different then. Today the tracks rest in two slabs perched on a rocky hill within a stone’s throw of the Colorado River, but when the tracks were made the area was a sandy shore of a lake.

The tracks were left by at least three different size classes of theropod dinosaurs. Two slabs of rock contain relatively small tracks paleontologists have assigned the name Grallator, slightly bigger tracks known as Eubrontes and even larger footprints, according to an interpretative sign at the site, were left by Allosaurus. This last attribution is probably a mistake. Allosaurus lived later in the Jurassic—around 155 million to 150 million years ago—and, unless an animal dies in its tracks, paleontologists can’t be certain what species created them. That’s why tracks are given their own names. In fact, it is possible that at least some of the tracks were made by dinosaurs of the same species but belonging to different ages. We may never know for sure, but the Potash Road tracks are still wonderful monuments from a time when dinosaurs were at home in Utah. I can’t wait to visit more of them.