Yellow and orange swirls color a chunk of Navajo sandstone in Grand Staircase.
The hiking route to Yellow Rock is unsigned and unmarked, like many of the trails in Grand Staircase-Escalante National Monument, Utah. Credit: Mary Caperton Morton

Southern Utah is blessed with five spectacular national parks, but in recent years, two remote and off-the-beaten-path national monuments stole international headlines when their boundaries were established, slashed, and then restored. Created to protect a wealth of geological, paleontological, archeological, and cultural resources, Grand Staircase-Escalante and Bears Ears National Monuments represent two of the last untrammeled natural laboratories in the American Southwest.

“Every field season, you know beyond a shadow of a doubt that you’re going to go out and find things that are totally new to science.”

People have been living in southern Utah for thousands of years, but the famously rugged canyon country was one of the last areas in North America to be explored and mapped. Even today, few roads traverse the region, and trails are often unmarked. But for those intrepid scientists who brave the backcountry to seek needles in this geological haystack, the rewards are bountiful: Fossils have been found in 20 of the 24 geological formations preserved in Grand Staircase. And many of those finds are unique. “Every field season, you know beyond a shadow of a doubt that you’re going to go out and find things that are totally new to science,” said regional district paleontologist Alan Titus.

Over the past 20 years, this prolific fossil record has painted one of the clearest pictures scientists have of Mesozoic ecosystems and the overarching role of climate change, which influences everything from the thickness of geologic layers, to patterns of fossil preservation, to pockets of regional biodiversity, to the future of a dry-and-getting-drier desert.

Descending the Staircase

In many ways, a “grand staircase” really is the best way to visualize the geology of this region, which descends in a series of mesas, cliffs, and canyons from the top step at 3,447-meter-high Brian Head ski area to the North Rim of the Grand Canyon 240 kilometers away.

The complex geology of this region is best described as a grand staircase that descends from Brian Head, Utah, to the North Rim of the Grand Canyon in Arizona. Click image for larger version. Credit: Peter J. Coney, Dick Beasley, Zion Natural History Association, Wikimedia

“Grand Staircase-Escalante National Monument is by far the biggest monument in the [contiguous United States, or lower 48], but the geologic feature is even bigger than the monument,” said Eric Roberts, a sedimentary geologist and paleontologist at James Cook University in Australia who has worked extensively in Grand Staircase.

Jutting into the skyline 240 kilometers to the east of Grand Staircase, Bears Ears is named for two 2,700-meter-high twin buttes that rise above the disorienting landscape, providing distinctive navigational beacons to ancient and modern travelers alike.

If Utah’s five national parks (Arches, Canyonlands, Capitol Reef, Bryce Canyon, and Zion) are shining jewels in the public lands crown, Grand Staircase-Escalante and Bears Ears National Monuments remain diamonds in the rough. Over the past 15 years, I’ve been exploring deeper and deeper into Utah’s canyons, graduating from easy, well-marked day hikes in the national parks to multiday off-trail backpacking trips in the national monuments.

The author summits Castle Rock, the highest point in the southern part of Grand Staircase, with Bryce Canyon and the Kaiparowits Plateau in the distance. Credit: Mary Caperton Morton

Of all the places I’ve hiked in all 50 states, nowhere offers the feeling of wild exploration, discovery, and life-or-death self-sufficiency like Grand Staircase and Bears Ears. If you can make it out there, you can make it anywhere on Earth. Climbing the Grand Staircase and treading between the Bears Ears, I’ve learned some of my most indelible backcountry lessons by getting lost, running out of water, and crossing paths with bears and mountain lions and barefoot human tracks. Over the years, I’ve gleaned enough hard-earned desert intuition to know how to blaze an off-trail loop and where to find water, good campsites, seldom-seen Ancestral Puebloan ruins, rock art panels, and my way back home.

Black bear tracks line the mud of Cottonwood Wash, a tributary of the Paria River. Credit: Mary Caperton Morton

In October, my best backpacking buddy and I met near the ghost town of Old Paria for a long loop from the Paria River, up and over Yellow Rock to Sam Pollock Arch, to the top of Castle Rock (the highest point in the southern part of Grand Staircase-Escalante National Monument), and back through the Paria Box. In 4 days, we saw no other people and more black bear tracks than human footprints.

With no marked trails or fresh footprints and very few cairns (rock piles) to follow, we navigated by constantly triangulating our position between handrails, distinctive large-scale features in the landscape like the Paria River, and Yellow Rock. With years of off-trail experience between us, we had no trouble making our loop and even summited Yellow Rock twice, once during the day and then again for the full moonrise, cooking dinner using rainwater filtered from a large pothole on the summit.

Exploring Grand Staircase often requires that you be able to navigate without the benefit of marked trails and routes. Credit: Mary Caperton Morton

In December, I met a pilot friend in Monticello for another off-trail adventure to find a cliffside ruin he spotted from the air. We drove his Subaru on a spectacular forest road that curves into the backcountry of Bears Ears, behind the Abajo Mountains. When we hit a sandy washout, we left the car behind and set out on foot to drop into a branching canyon system, with the twin buttes of the Bears Ears in our sight line.

Can you find the granary hidden on this south-facing wall? Credit: Mary Caperton Morton

At the bottom of the deepest canyon, we entered another world of lush greenery and running water, an oasis in the desert where ancient people once thrived. Following a debris-choked side canyon upstream, we kept our eyes trained on the warm, south-facing wall, where Ancestral Puebloans tended to build their dwellings and storage structures. Sure enough, after scrambling up a rocky outcrop, the ruin appeared, tucked away on a ledge with no easy access. A ladder of lashed-together wooden sticks stood upright in the middle of the ruin, waiting for hundreds of years to be lowered down to the next watchman. We didn’t try to get closer; we were running low on daylight, and some places are too sacred for modern footprints.

When Dinosaurs Ruled Utah

Today, hot and dry southern Utah doesn’t support much large fauna, but the region was once populated by the planet’s largest land animals. The most famous layers of the Grand Staircase are made up of sediments laid down during the Mesozoic Era, starting around 250 million years ago.

During this time period, Earth was much hotter, warmed by extremely high levels of carbon dioxide in the atmosphere. “Even though this region was actually farther north than it is now, the Earth was a hothouse then, and this part of Utah would have looked and felt more like the lush, wet bayous of Louisiana,” said Randy Irmis, curator of paleontology at the Natural History Museum of Utah.

The Late Cretaceous in what is now southern Utah was a wet, green world more like the bayous of modern day Louisiana. Credit: Raúl Martín

The Mesozoic fossil record begins in the early Triassic, with a “fairly good record in the Chinle Formation,” Irmis said, including a nearly fully articulated skeleton of Poposaurus, a bipedal crocodilian recovered from the Circle Cliffs. The fossil record gets “a little thin” heading into the early Jurassic because of a shift toward a more arid climate that was not conducive to preserving fossils, Titus said. “We know the place was crawling with critters because we find their track [footprint] fossils everywhere, but their bones didn’t survive long enough to become fossils.”

Ornithopod tracks from the Late Cretaceous dwarf human feet in Grand Staircase. Credit: Mary Caperton Morton

Starting in the Middle Jurassic, however, conditions became ideal for forming thick stratigraphic layers chock full of fossils. “The paleogeographic location of what is now the Grand Staircase was located just east of a huge mountain range that was shedding immense amounts of sediment into the adjoining basin, making for quick burials,” Titus said. A wetter climate and higher water tables also helped create ideal conditions for fossil preservation.

The result is an almost uninterrupted sequence dating from about 100 million years ago almost all the way to the extinction event at the end of the Cretaceous about 30 million years later, Titus said. “It’s unique to see an almost continuous terrestrial fossil record, and the fact that it produces good fossils from bottom to top is also very unique. In this one place you can track the evolution of the biosphere from the inception of flowering plant communities to the evolution of dinosaurs into birds.”

When Climate Ruled the Dinosaurs

These Cretaceous layers are exceptionally thick; on the Kaiparowits Plateau, one particularly fossil rich section runs nearly a kilometer deep, representing a period of very rapid sedimentary deposition over only about 2 million years. “These thick sections actually represent very thin slices of geologic time, giving us a rare opportunity to study patterns of ecological, environmental, evolutionary change as they were happening,” Roberts said. “There are very few places in the world where you can do that.”

Teratophoneus is a genus of tyrannosaurid unique to the Late Cretaceous layers of Grand Staircase. Credit: Alan Titus

Not only are the Late Cretaceous fossil record prolific and the quality of preservation “mind-blowing,” but this record is also strikingly unique from every other Late Cretaceous record in North America, Titus said. “When we started discovering fossils here, we assumed they would be similar to dinosaur fossils found at other Late Cretaceous sites in North America, but much to our surprise, these animals are radically different.”

“As far as we know, there weren’t any physical barriers to migration, and yet each basin has its own unique assemblage of animals,” Titus said. “The reasons for this have been debated for some time, but we now think that climate was driving this diversification, as the animals adapted to thrive within the vegetation and forest resources of their region.”

The dinosaurs of Grand Staircase likely occupied a tropical biogeographic region, whereas the dinosaurs of what are now Montana and Alberta lived in a more temperate zone. The abundance of plant fossils found in Grand Staircase corroborates this theory, demonstrating “remarkably high species diversity, similar to the modern Amazon Basin,” Titus said. “But you also have to keep in mind, flowering plants were not yet the dominant overstory yet. These would have been dense, lush tropical conifer forests populated by huge, elephant-sized animals.”

The Unicorns and Rainbows Quarry on the Kaiparowits Plateau has produced some of the most exciting finds in paleontology in the past year, including a family of tyrannosaurs. Credit: Alan Titus

Spectacular dinosaur discoveries, such as the potential family unit of tyrannosaurs unearthed in the monument’s Rainbows and Unicorns Quarry, tend to hog all the headlines, but Grand Staircase is also famous for its fossil record of small mammals, said vertebrate paleontologist Jeff Eaton, professor emeritus at Weber State University. “The little stuff isn’t as glamorous as the dinosaurs, but you can get thousands of specimens in a field season. The small guys tell us a lot about how the climate and the ecosystem was changing.” Grand Staircase is known for hosting a diverse record of some of the earliest marsupial fossils. “We also see a very rich record of other mammals, frogs, and lizards,” he said.

The Saga of Bears Ears

People have been living in southern Utah for at least 15,000 years, and possibly longer, but these early residents left few clues about their lifestyle or existence. Rock art offers some of the earliest evidence of their presence, with panels near Moab and Bluff depicting mammoths or mastodons, suggesting that ancient people shared the landscape with the behemoths, which went extinct between 13,000 and 11,000 years ago.

Around 3,500 years ago, people began shifting from foraging into farming, and more evidence of their seasonally nomadic lives begins to appear on the landscape, including baskets; pottery; and stone structures such as pit houses, pueblos, and cliff dwellings. With year-round fresh water and rich alluvial fans for farming, by 1250, the area between Bears Ears and the San Juan River had become one of the most populous regions of North America, home to around 30,000 people now known as the Ancestral Pueblo.

More than 100,000 archeological sites have been identified in Bears Ears National Monument, and the area has long been held sacred by the Hopi Tribe, Navajo Nation, Ute Mountain Ute Tribe, Ute Indian Tribe, and Pueblo of Zuni as a key piece of their ancestral homelands.

The deep canyons of Bears Ears were once home to tens of thousands of people. Credit: Mary Caperton Morton

The advocacy of the Bears Ears Inter-Tribal Coalition, an alliance made up of members of all five tribes, helped lead President Obama to establish the 5,500-square-kilometer Bears Ears National Monument in December 2016. But the triumph was short-lived. A year later, the Trump administration slashed the boundaries of the monument, reducing it by 85% to two smaller discontinuous units. At the same time, the administration also reduced the size of Grand Staircase-Escalante, established by President Clinton in 1996, by 50%.

“When the cuts came along, it didn’t just affect the boundaries, it affected funding and decades of coordination that helped make the scientific efforts so productive.”

“National monuments are pieces of land that are set aside for special scientific or historic or archeological purposes,” said David Polly, a paleontologist at Indiana University and former president of the Society of Vertebrate Paleontology. “The initial management plans really emphasized scientific research and provided a lot of funding. When the cuts came along, it didn’t just affect the boundaries, it affected funding and decades of coordination that helped make the scientific efforts so productive.…It was a big blow to research.”

In October 2021, President Biden restored the boundaries of both monuments, but new management plans have not yet been released. “Every time the boundary changes, we have to revisit the rules and regulations for administering the lands,” Titus said. “Hopefully, the new plan is supportive of the scientific interest in this place. I’m optimistic that everybody will still want to come play in our sandbox.”

It’s unlikely, however, that the new plan will emphasize further development of the monuments into more-tourism-friendly parks—a relief to those of us who want to see the last remaining wild places stay wild. “The goal for this area has always been wilderness,” Polly said.

Climate Is King

Climate played a starring role in the formation and evolution of the Grand Staircase region; the area offers an invaluable natural laboratory for studying climate change throughout the geologic record and into the future, Titus said. “Researchers here are looking at every aspect of natural science that you can imagine, and we have a fairly good baseline of animal and plant diversity and their geographic contexts, from the fossil record into modern times.”

Since the last ice age, paleoclimate data gleaned from plant fossils, pollen, lake cores, and tree rings show that the area has gradually transitioned from cooler and wetter to warmer and dryer. When large human populations were living in this area, it was much wetter and greener than it appears today, with large alluvial fans of rich soils where people could grow squash and corn.

Between 1,000 and 700 years ago, southeast Utah went through a series of megadroughts and flash floods that stripped away the alluvial fans. Without the nutrient-rich soil, opportunities for agriculture plummeted. The resulting food scarcity is thought to have inspired the Ancestral Puebloans to build dramatic cliff dwellings and inaccessible granaries as raiding and conflict became more common. Eventually, tens of thousands of people abandoned the area en masse, moving east and south into what are now Arizona and New Mexico.

Many ruins in Bears Ears National Monument appear to be defensive structures built in hard-to-reach places. Credit: Mary Caperton Morton

This inhospitable climate trend continues. “Utah is certainly warming and drying,” Eaton said. “When I moved here 30 years ago, it was rare we had a day above 90°. Last year we had many days over 100. Monsoon rainstorms used to be a traditional part of the climate here. Now they’re almost nonexistent, and we get very little precipitation.”

Climate change is nothing new, but “what is happening now is happening faster and at a higher magnitude than it has in the past,” said Allison Stegner, a paleoecologist at Stanford University. In the past, during periods of change, plants and animals were able to migrate to seek out new “sweet spots,” Titus said. But with so many physical barriers on the landscape such as roads, fences, and human infrastructure, species have fewer places to go to beat the encroaching heat.

“We wouldn’t be so worried about climate change if species were able to freely move across the landscape,” Stegner said. “From the perspective of fostering biodiversity and functioning ecosystems, we can’t be randomly expanding and contracting protected areas. We need to focus on connectivity and making sure species can move where they need to go.”

From Dust to Sandstone, Back to Dust

The layers of Grand Staircase continue to erode and expose traces of ancient landscapes and climates. Credit: Mary Caperton Morton

With its thick layers of relatively soft sandstones and mudstones, the Grand Staircase is one of the most highly erosional landscapes in North America. “This is a rapidly evolving landscape, where you can literally see erosion happening before your eyes,” Roberts said. Rapid change is part of what makes the area such a boon to paleontologists, as new fossils are constantly being uncovered. “In the future, the landscape will continue to evolve and expose more fossils and create more opportunities for paleontologists,” he said.

The region will also likely keep getting hotter and dryer, and western snowpack projections are expected to dwindle. “If it’s too warm to store snow, that will be devastating for the West,” Eaton said. “Over the very long-term, I can’t assess if there would be some new tectonic pattern that would rejuvenate tectonics and restart uplift of the region. But otherwise, sediments will continue to erode, and these magnificent landscapes will be slowly beveled down. I’m glad I get to enjoy them now because they will not last forever.”

—Mary Caperton Morton (@theblondecoyote), Science Writer

Living in Geologic Time is a series of personal accounts that highlight the past, present, and future of famous landmarks on geologic timescales.

Citation: Morton, M. C. (2021), When climate ruled the dinosaurs of Grand Staircase, Eos, 102, https://doi.org/10.1029/2021EO210692. Published on 27 December 2021.