Discover Utah and Explore the Geodiversity and Fossils of Arches National Park
- Wayne Munday
- Apr 16
- 6 min read
Sip back and discover Utah and explore the geodiversity, fossils and dinosaurs of the Arches National Park located in the Moab region of south east Utah. A 6 hour drive west from Denver on the I-70 or a 4 hour drive south east from Salt Lake City on the US-6. This is an area is known for its dramatic desert scenery. Officially recognised in 1929 by President Herbert Hoover it became a national park in 1971. The Arches National Park covers and area of over 308 Km2 and is primarily known for its more than 2,000 natural sandstone arches and fossil record. The Arches National Park red rock colour indicates iron rich minerals that have oxidised upon exposure to air. This unique landscape has played its part as the cinematic backdrop for Indiana Jones and the Last Crusade and Thelma & Louise. The Arches National Park human history dates back to 10,000 years beginning with the Desert Archaic peoples and continuing through to the Ancestral Puebloans and Fremont cultures until the Middle Ages. The region is a hub for outdoor recreation like hiking, biking, and climbing and has an industrial significance as a source of subsurface potash and salt deposits concentrated in the areas anticlines and salt domes.
Despite the harsh conditions the Arches National Park sustains a vibrant biodiversity making it a haven for wildlife adapted to the extremes of temperature, ruggedness and water scarcity. The Arches National Park supports a number of mammals, birds, reptiles, amphibians and invertebrates each uniquely adapted to thrive in its arid environment. Among the most recognisable mammals are bighorn sheep which navigate rocky terrain with ease and mule deer can often be spotted grazing during twilight hours.
Smaller mammals such as kangaroo rats and desert cottontails are common particularly at night and in brushy areas. The Arches National Park is also home to elusive predators like mountain lions and more frequently seen coyotes as well as other small mammals including woodrats, skunks, ringtails, foxes and bobcats.
The Arches National Park has several reptile inhabitants including Collared lizards that are easily identified by the distinctive dark bands around their necks. Western rattlesnakes are common in the region as well as the less prevalent midget faded rattlesnake. Both possess venom so watch your step!
The Arches National Park also features ephemeral pools or temporary bodies of water that support aquatic species such as fairy shrimp and tadpoles during brief wet periods. Amphibians, while less visible, are present in the form of spadefoot toads that can survive prolonged dry spells by burrowing underground and only emerge when conditions permit when wetter.
Birdlife in Arches National Park is diverse and includes peregrine falcons and golden eagles that prey on smaller animals. Of particular note are endangered and protected species such as the Southwest Willow Flycatcher. The Arches National Park is also home to over 745 identified plant species including grasses, cacti, deciduous and evergreen trees.
The geology of the Arches National Park spans over 300 million years of tectonic shifts, sedimentation, sea level changes, erosion, and salt movement. Most arches are found in Jurassic Period aged sandstone especially the Entrada and Navajo formations.
Tectonic activity during the Middle to Late Jurassic warped the Moab region forming anticlines and synclines that created cracks and joints in the underlying rock. During the Cretaceous Period an inland sea repeatedly transgressed and regressed laying down sediments. Then between 70 - 35 million years ago during the Laramide Orogeny the US western interior was uplifted and so started the process of arching the landscape.
Then approximately 15 million years ago the entire area uplifted again forming the Colorado Plateau and the fractured sandstone was exposed to the elements of water, wind, and freeze-thaw cycles. Continued erosion over time formed sandstone fins or narrow residual wall that would erode and fall away to become arches.
Arches are categorised by formation type including Freestanding Arches like Delicate Arch and Double Arch that stand independent of rock walls. Pothole Arches such as Pothole Arch that form when surface depressions merge with alcoves and Cliff Wall Arches including Park Avenue Arch and Biceps Arch that emerge along rock faces.
The Arches National Park as well as its dramatic sandstone arches and desert landscape holds and extensive and varied fossil record. Spanning from the Paleozoic to the Mesozoic Era's the fossil record tells a story of past marine and terrestrial ecosystems.
Both the oldest fossils and oldest exposed sedimentary rock layer at Arches National Park is found in the in several anticlines of eastern Utah. Known as the Paradox Formation it is made up of gypsum, anhydrite, salt and interbedded with shale, sandstone and limestone.
The Paradox Formation dates back to the North American Desmoinesian Age between 301 - 330 million years ago during the Middle Pennsylvanian subperiod of the Carboniferous Period and has a fossil record that includes Rugose corals, lacy and branched bryozoans, productid brachiopods, crinoid stems and trilobites.
During the Desmoinesian Age the Moab was submerged under a shallow sea that was part of a much larger regional sea and an extension of the earlier Mississippian Sea which had covered Utah during the Mississippian Period. The Paradox Formation was deposited in the Paradox Basin formed by tectonic forces that also uplifted the Rocky Mountains. This basin was intermittently connected to the open ocean and experienced repeated cycles of fluctuating sea levels from the transgression of sea water flooding the land and regression from the withdrawal of the sea exposing the former seafloor.
These the phases of transgression and regression created evaporite cycles whereby evaporation led to hypersaline conditions and the precipitation of minerals where dissolved mineral elements would become separated out from the water to be accumulated as chemical sedimentary rocks such as Calcite, Gypsum, Anhydrite, Halite and finally potash. In total the Paradox Formation had at least 29 evaporite cycles.
The Paradox Formation is generally buried beneath younger rock layers but is exposed or lies near the surface along anticlines or arched folds caused by the upward flow of underlying salt due to its low density and plasticity under pressure. The Paradox Formation does preserve assemblages of marine vertebrate and invertebrates that also record the transition from marine to terrestrial environments.
During the Mesozoic Era the fossil record shifts to a predominantly terrestrial ecosystem that includes dinosaurs. The Cedar Mountain Formation formation that lays on top of the Morrison Formation and is a key source of such fossils and is especially notable for its abundant dinosaur trackways such as the Mill Canyon Dinosaur Tracksite. These tracks are attributed primarily to bipedal and carnivorous theropods including Utahraptor, Moabosaurus, and Gastonia.
The Cedar Mountain Formation dates from approximately 127 - 98 million years ago, spanning the Late Aptian and Early Albian stages of the Early Cretaceous Epoch. The formation was not marine but fluvial deposited by rivers, lakes and on floodplains. The Cedar Mountain Formation is tied to the Sevier Orogeny part of the Cordilleran orogenic belt.
The Kayenta Formation also contributes significantly to the Park’s fossil record and yielded the first dinosaur partial skeleton fossil found within this formation in Utah belonging to a theropod related to Dilophosaurus. Beyond these, several other geologic formations within Arches National Park including the Moenkopi, Chinle, Wingate, and Navajo Sandstone contain additional dinosaur track sites.
The Wolfe Ranch Petroglyph panel in Arches National Park is a significant Native American rock art site prominently displayed along the Delicate Arch Trail. The petroglyphs are attributed to the Ute and possibly Paiute tribes. These carvings reflect the cultural and historical presence of Indigenous peoples in the region during a time of major transformation, particularly following the introduction of horses in the mid-1600s, which profoundly influenced Ute methods of hunting, travel and daily life.
The panel features stylized depictions typical of Ute artwork, including a horse and rider surrounded by bighorn sheep and what appear to be dogs, representing hunting scenes with clear symbolic resonance. The inclusion of mounted figures confirms the petroglyphs’ relatively recent origin compared to older, more abstract rock art found elsewhere in the South West of the United States.
Visitors can easily view the carvings from a designated point along the 4.8 Km moderately strenuous hike at Delicate Arch Trail making the panel a prominent cultural feature within the park’s natural landscape. The petroglyphs serve as a vital record of Native American life, belief systems, and adaptation in a changing environment. The imagery offers insights into the spiritual and societal dynamics of the Ute and Paiute people, connecting present-day viewers to centuries-old expressions of identity, subsistence, and cultural memory. As such, the Wolfe Ranch Petroglyphs are not merely artistic artifacts but enduring symbols of Indigenous resilience and heritage, embedded within the geological and historical fabric of Arches National Park.
