The Mill Canyon Dinosaur Tracksite
The Moab area is blessed in many ways. World-class scenery, two national parks, two state parks, an incredible range of opportunities for outdoor activities, and a vibrant small-town community.
Southeastern Utah is also geologically blessed. Not only is there the classic desert landscape with cliffs and canyons, but the rocks exposed in the area tell the geologic history of this region over a time span of more than 200 million years. The Moab area is also a hotbed for geologic research.
Most of the rocks exposed in southeastern Utah were deposited during the Mesozoic, better known as the Age of Dinosaurs. Many of the rock layers (formations to geologists) here were deposited in environments in which dinosaurs lived; that is, mostly in continental environments including along rivers and their floodplains. Therefore, Moab’s geologic story also includes an incredible dinosaur fossil record, and it includes places where you can see dinosaur fossils in situ (e.g., in place in the rocks where they naturally occurred). For most people, it is thrilling to see dinosaur fossils in a natural history museum. But there is something extra special in seeing them in a natural exposure like you can on interpretive dinosaur trails managed by the Bureau of Land Management, the agency that manages most of the public lands near Moab.
Dino tracks
The Mill Canyon Dinosaur Tracksite was first developed about 10 years ago and features a boardwalk where people can view dinosaur tracks and other traces exposed in the bedrock below. Fossil tracks were first reported at that location in 2009. Subsequent research and further excavation has revealed that this site is one of the ten most important dinosaur tracksites in the United States.
The Mill Canyon Dinosaur Tracksite contains more than 200 tracks of dinosaurs and other animals. Most tracks are from dinosaurs, including those from therapods (bipedal three-toed dinosaurs), sauropods (long-necked herbivores), ankylosaurs (armored plant-eating dinosaurs), and ornithopods (bipedal herbivores). Bird tracks as well as an impression of a crocodile sliding into the water are also present. The tracks were left on an algae-covered mudflat near the shore of a shallow lake.
Conditions have to be just right for animals tracks to be preserved in the rock record. Think of the footprints you make when walking on the beach. Those left in dry sand are indistinct as are those left in soft mud. A good track-making surface is both soft and firm enough for a clear impression to be made. Then the tracks must get buried by later sediment without being destroyed by water currents, other animals trampling them, and other factors.
The Dinosaur Bone Trail features the type of fossils that people most often associate with these giants of the past—their bones. Along this trail, there is a variety of dinosaur bones, including those from the legs, ribs, and tail, all encased in sandstone. This sandstone layer contains pebbles and other evidence that indicates that it was deposited in river channels. At the time, it was a lush tropic environment, much different than high desert climate of today. The dinosaurs likely lived along the streams and may have died along its banks. The bones may then have been carried by stream currents to their final resting places that are now exposed along the trail.
The Mill Canyon Dinosaur Trail
Fossils of Allosaurus, Camptosaurus, Stegosaurus, and Camarasaurus are present on the Bone Trail. Allosaurus, the Utah state fossil, was a fierce predator. This therapod could reach lengths of nearly 40 feet, and had fearsome cutting teeth. The other dinosaurs are all herbivores. Camarasaurus was a large sauropod that stood on sturdy pillar-like legs. Camptosaurus and Stegosaurus were smaller; Stegosaurus’ upright armored plates are well-known, and Camptosaurus was a medium-sized dinosaur that sometimes walked on two legs and sometimes on four.
Not only are these fossils bones older than those at the tracksite, the Bone Trail is also older. Originally developed in 1986, it was one of the BLM’s first interpretive sites showcasing paleontological resources. Opportunities to see dinosaur bones “in the wild” are rare and this trail is notable both for the number of fossils and its excellent interpretive signs.
Together, these two trails provide a dynamic way to look into the deep geologic past—all the way back to the time when dinosaurs roamed the planet.
Sauropod rib bones
Both trails are located about 15 miles north of Moab, and reachable by a graded dirt road off of Highway 191. (Note: sometimes loose sand causes the road to the Bone Trail to be in 4WD condition. It is about 0.8 miles from the Tracksite to the start of the Bone Trail for people who may need to walk the road.)
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A self-described “rock nerd,” Allyson Mathis is a geologist, informal geoscience educator and science writer living in Moab.