Part of the upper section of the famous quarry wall at Dinosaur National Monument, Utah.
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Photo by Brian Switek.
Part of the upper section of the famous quarry wall at Dinosaur National Monument, Utah.

A Monumental Murder Mystery

Scorched by the relentless heat and harried by the biting insects that are inherent to eastern Utah summers, fossil prospector Earl Douglass was finding himself increasingly frustrated as he trudged over Jurassic sandstone in search of a perfect dinosaur. What we really wanted to do was look for prehistoric mammals. Ancient beasts were far more exciting to Douglass than any enormous reptile, but his employer – the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania – didn’t want brontothere jaw fragments or more rhinoceros teeth. They wanted a show-stopping sauropod – an imposing long-necked, heavy-bodied dinosaur – for their exhibit halls.

The Carnegie’s field man got his change of orders on August 4th, 1909. That day, Douglass later wrote in his journal, he received a letter from William Jacob Holland – director of the museum – that Douglass was to stop puttering around in search of mammals and get to the dinosaurs. “He seemed somewhat disgusted, made me a little hot. Seemed to think I wasn’t doing much,” Douglass lamented to the pages.

Vernal, Utah’s climate didn’t make Douglass any cooler. On August 8th, after arriving among the colorful Mesozoic exposures near the Utah-Colorado border, Douglass took a stroll through the cracked and sun-beaten landscape to take a few photos. He didn’t have the most relaxing walk:

It was hot as blazes. It seems to me that it is always hot in this country, but I suppose it isn’t in the winter, and when you get in a cool place near the water and in the shade the flies and mosquitoes and gnats are there to persecute you.

Well I walked a little way and stopped in the shade and lay down and had a nap, and the ants crawled all over me.

Fieldwork among the hills didn’t bring any relief, especially since Douglass only got his start to the “dinosaur beds” in the afternoon heat of the 10th. The fact that local prospectors had already taken the best of the exposed bones from the first site he visited was a further insult. Other sites only seemed to preserve fragments or the occasional isolated tidbit.

The Carnegie wanted a monster, and Douglass was only stumbling over scraps. Even when Douglass found signs of fossils he hoped were held safe within the stone, he was disappointed. On the 16th, he started working a layer of dinosaur bones. “Found that it extended further than I supposed,” Douglass wrote, “but when I dug into it, it was disgusting. The bones were terribly broken up and seemed as if they had been churned up. … Felt rather discouraged.”

But, following his director’s rebuke, Douglass kept searching for dinosaurs. He wasn’t going to fritter away any more time poking away at fragments, he declared to his journal, but would only dig in when there was hope of uncovering something good. And that’s exactly what Douglass found on the 17th. Clambering over thick, tilted, tan sandstone laid down by a Jurassic floodplain, Douglass spotted part of a tantalizing tail. “At last, in the top of the ledge where the softer overlying beds form a divide, a kind of saddle, I saw either of the tail bones of a brontosaurus in exact position. It was a beautiful sight,” he recounted.

The next day, Douglass dug in at what must have been a frantic pace for fieldwork. He needed to know if there was more of the animal in the rock or the tail was the dinosaur’s last sign-off before totally eroding. As Douglass broke and chipped and flipped sandstone out of the way, parts of the hip and thigh bones of the enormous sauropod came into view. After a reserved reaction to the initial discovery – at least, as far as Douglass recorded the find in his notes – his imagination started to revel in the image of an articulated skeleton just below the surface.

It is natural for one to picture finding a whole skeleton, head and all. Things look so good that to find a whole skeleton is almost unavoidable but one is liable to be disappointed. But if it were whole, the rest of it!! My!!!

Little did Douglass know that he had found the very tip of a vast Jurassic boneyard that would become not only a major contribution to paleontology, but a national treasure. The gaggles of parasol-shaded onlookers who started to come out from Vernal to see what he had found were just the barest glimmerings of the carloads of visitors who would eventually return to the same place to view scads of dinosaur bones preserved in place – the embodiment of a “living museum” Douglass dreamed of as he spent summer after summer excavating his treasure trove.

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Photo by Brian Switek.

Douglass excavated the skeletons the Carnegie so fiercely desired – the natural history of Utah is still on display thousands of miles away in Pennsylvania – but he dreamed that much of the snarl of bones would remain in place to give visitors an unprecedented view of Jurassic life and death. In 1957, five decades after being officially established as Dinosaur National Monument, a glass building was built over the famous quarry wall so that visitors could see continuing excavations. By 2006, shifts in geology were literally tearing the building apart, but an infusion of federal funding stimulated the construction of a new, more stable museum that reopened on October 4th, 2011.

I was there for the re-dedication of the quarry wall. The first time I visited the national park in 2009, the building was closed. Two years later, after I moved to Utah and spent my first summer feeling Douglass’ frustrations all too well as I searched the park’s Triassic rock for dinosaurs, I still had to be patient – protective barriers covered much of the fragile wall as construction neared completion. After spending so much time in the shadow of Douglass’ quarry, I made sure to be first in line when the new building finally opened.

Strewn across the sandstone slope, the dinosaur bones are gorgeously macabre. Decades of careful preparation work – now finished – revealed articulated stretches of neck, legs dissociated from their bodies, the grim smile of Camarasaurus skulls, and a gorgeous mess of isolated bones cast over the rock face.

All the Jurassic celebrities are here. Titans with ridiculously-long necks such as Apatosaurus, Barosaurus, Camarasaurus, and Diplodocus; little, bipedal, beaked herbivores such as Camptosaurus and Dryosaurus; the exceptionally-armored Stegosaurus; and the trio of apex flesh-rippers Allosaurus, Ceratosaurus, and Torvosaurus – these are the dinosaurian celebrities found in the messy collection of a magnificently diverse Jurassic ecosystem. Together the fossils create a scene of tragic Jurassic death, but have been so lovingly and intricately prepared that the beauty of time, evolution, and ancient life eclipse the fact that visitors are looking at a mass grave.

How did so many dinosaurs – and smaller, less-recognizable critters featured in the museum’s lower gallery – come to be buried in one place? Douglass’ quarry forms a census of Jurassic Utah, but, like other bonebeds of comparable age found just a few hours away in the Beehive State, the bony Dinosaur National Monument morass came together because of unique historical quirks.

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A logjam of bones, including tail pieces, in the Dinosaur National Monument quarry wall. Photo by Brian Switek.

Writing in the May issue of the Annals of the Carnegie Museum, Utah State University Eastern paleontologist Kenneth Carpenter has summarized the story of the Dinosaur National Monument quarry – from discovery to the fate of the animals entombed there. Rather than being a testament to a single and devastating die-off during the heyday of dinosaur giants, the quarry contains the bones of dehydrated dinosaurs that were dead by the time seasonal rains returned to wash the remains together over and over again.

The scores of dinosaur bones that peek out from the quarry were deposited by a Jurassic river system. That much has been plain since Douglass’ day. The composition of the sandstone, freshwater mollusks, and other clues clearly indicate that the dead dinosaurs – intact or in parts – were tumbled together by flowing water. But this doesn’t explain why the dinosaurs died in the first place, or what conditions led their bones to be swept up together. The backstory of the bones is harder to tease out of the rock.

Tossed together, the skeletons and isolated pieces in the quarry present a Jurassic cold case. No one knows for certain what killed so many dinosaurs, or even over how long a time span. But the distribution and details of the fossils have let paleontologists narrow down the possibilities. The prime suspect is drought.

Drawing from geological and geochemical evidence, reconstructions of the Jurassic habitat around the quarry and at other Morrison Formation sites envision a seasonal floodplain affected by distinct wet and dry seasons. And during those times when watercourses shrunk back and vast carpets of ferns dessicated, herbivores in the area may have succumbed one by one from lack of water and nourishment. Carnivores wouldn’t face the same limited menu in these conditions, but the scarcity of water or disease may have killed the likes of Allosaurus.

Whatever their individual causes of death, however, dinosaurs likely concentrated around dwindling or totally evaporated sources of water. When they perished, their bodies littered floodplains near vanished lakes and rivers. And as the next wet season began to rain down, the renewed flows transported and collected many of their remains, burying them beneath the sandy sediment that would eventually harden and preserve what was left of them for the next 150 million years. This did not happen once, but multiple times as the seasons teetered from dry to wet and back again.

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Although dominated by herbivores, there are carnivores in the Dinosaur National Monument quarry too – here is a skull of Allosaurus in the new quarry museum. Photo by Brian Switek.

In their own way, the dinosaurs helped create the quarry. On the basis of experiments with bone casts, water, and sediment, Carpenter reported that the carcasses of large dinosaurs diverted water flow, scouring the riverbottom and altering the ways in which others of the dead and their body parts would be scattered over the sediment. And as large dinosaurs started to fall apart – skulls and lower limbs tumbling away first, while stretches of vertebrae and heavier limb bones sticking together by virtue of ligament connections or even their sheer weight – the way the river snaked and eddied around the bodies continued to change. Rivers did not simply pull a sedimentary blanket over dinosaurs and tuck them in. Bones and body parts influenced the burial of the drought-stricken dinosaurs.

This is hardly the last word on what created one of the world’s most stunning dinosaur monuments. Part of the problem in studying the quarry, Carpenter noted, is that massive stretches of the original bonebed were removed, many fossils were sent to institutions around the country, and there are still specimens that remain unprepared. To start to understand what transpired over many Jurassic seasons, the seemingly insurmountable task of virtually reconstructing the full quarry is a major initial step. Yet, even then, there’s still much we must learn about the ecology of the Jurassic, the biology of dinosaurs, and what causes mass mortality among living animals.

There will be no single conclusive piece of evidence that cinches the solution to the quarry’s mystery. The boneyard stands as a challenge to our ability to envision and understand fleeting moments of prehistoric time that we can only just barely touch through the signs left in rock and bone.

[You can read more about Dinosaur National Monument, and the site’s importance to the “Brontosaurus” debacle, in My Beloved Brontosaurus.]


Carpenter, K. 2013. History, sedimentology, and taphonomy of the Carnegie Quarry, Dinosaur National Monument, Utah. Annals of the Carnegie Museum. 81, 3: 153-232