The Parking Lot Sauropod of Dinosaur National Monument: Part 1

By ReBecca Hunt-Foster, Dinosaur National Monument paleontologist

Recent parking lot construction work in Dinosaur National Monument revealed previously undiscovered fossils near the Quarry Exhibit Hall, marking the first fossil excavations in this portion of the Carnegie Quarry since 1924. This section of the park is located north of Jensen, Utah, in the northeastern portion of the state.

Background

Dr. Earl Douglass of the Carnegie Museum discovered what is now called the “Carnegie Quarry” (sometimes referred to as the “Douglass Quarry”) in August of 1909. He and his crew had 13 years of success digging at this Morrison Formation site north of the Green River and Jensen, Utah, collecting more than 317 metric tons of fossils and matrix between 1909 and 1922 (Beidleman 1964; Carpenter 2013). The remains of ten different species of dinosaurs, along with clams, turtles and crocodiles, were found in abundance and shipped back to Pittsburgh, where many are still on display at the Carnegie Museum of Natural History.

Excavation work was continued on the east side of the Carnegie Quarry in 1923 by the US National Museum of Natural History (USNM), and in 1924 by the University of Utah (UU). Notable discoveries from these areas are the Diplodocus and Camarasaurus currently on display in the Deep Time exhibit at the USNM, the rearing Barosaurus in the rotunda of the American Museum of Natural History in New York City, and one of the best Allosaurus skeletons and skulls known (DINO 2560), casts of which are on display at many venues, including the Salt Lake City airport. The real skull is on permanent exhibit at the Quarry Exhibit Hall (QEH, formerly the Quarry Visitor Center) at DINO, and the skeleton is part of the permanent DINO museum collections (Figure 1A).

Figure 1. A) Eastern extent of Carnegie Quarry map, after Carpenter (2013), Figs 9 and 10. Allosaurus (yellow). Barosaurus (cyan). Diplodocus (dark blue. Parking lot Diplodocus (light blue). Dotted line: eastern wall of Quarry Exhibit Hall. B) Extent of Morrison Formation Quarry Sandstone layer around the Quarry Exhibit Hall at Dinosaur National Monument (green; after Carpenter and Taylor 2025, Fig 3A). Fossil Discovery Trail (red). Scale bar: 200 meters, or 0.12 miles.

A) Carpenter, K. 2013. Annals of Carnegie Museum 81: 153–232. B) Carpenter, K., and L.H. Taylor. 2025. Geology of the Intermountain West 12: 25–74.

Fossil excavations at the Carnegie Quarry in DINO were halted from 1925 until the 1950s, with the official Quarry Visitor Center, a Mission 66 glass and steel structure, opening in 1958. Inside this building, visitors to the monument could watch as fossil technicians worked to expose fossils still embedded in the sandstone. The goal was to leave as many fossils in situ on the quarry wall as possible for visitors to see them exactly as they had lain for the past 150 million years. When this revealing work began to wrap up in the 1990s, excavations and paleontological investigations continued, but were conducted in other, less publicly viewable areas of the park.

Geology

The “Quarry Sandstone”—the unit of rock within the Brushy Basin Member of the Late Jurassic Morrison Formation in which the Carnegie Quarry is found—is not only present at the Carnegie Quarry but continues laterally east and west (see Carpenter and Taylor 2025 for a full explanation) and represents a braided river channel. It is also present along the Fossil Discovery Trail, located in Neilsen Gulch to the east of the QEH. This portion of the sandstone also preserves many in situ, “wild” fossils that have not been excavated or highlighted and are encased in the rock as they would have been during the 1909 discovery by Douglass, giving visitors an opportunity to see these fossils in their native and unaltered setting (Figure 1B).

Road Rehabilitation Project

In May 2025, an $11.2 million project to upgrade roads, parking areas, overlooks and more was scheduled to begin on the Green River and Quarry Access Roads from the Utah highway SR-149 boundary to the QEH. This work would cross Cretaceous and Jurassic bedrock and there was the possibility of encountering significant fossils. The park was able to bring on a seasonal paleontological assistant, Rudolph Hummel, to assist with the monitoring of the construction along the roadway during surface-disturbing activities.

The main area of concern was in and around the QEH. Since the Carnegie Quarry, encased by the QEH, is the reason the park was established in 1915, it was important that this area was closely monitored during the construction activities. While several fossils were found outside of the main QEH area, nothing of great significance was located. Work around the QEH parking lot was the main area of paleontological focus. The greatest concern was that this area was built upon the tailing pile from the historic quarry operations (Figure 2).

All rock material that was dug or blasted away was dumped off the eastern side of the quarry into what is known as Neilsen Gulch (where the Fossil Discovery Trail meanders through today). This dumping work continued into the 1930s, when the Civil Works Administration of Utah (1933–1934), the Transient Relief Service of Utah (1934–1935), and the Works Progress Administration (WPA, 1935–1940) worked to improve roads to the quarry, clearing debris, and removing the overburden that covered the bone-bearing layers of the Carnegie Quarry (Carpenter 2018; Rich et al. 2025; Figure 2).

A concern was that fossils overlooked in the blocks or removed debris, or fossils deemed not significant enough for historic collection work. could be found in these areas, in addition to the possibility of encountering the Quarry Sandstone in situ. The road to the QEH, and the QEH itself, were closed from September 8 to late October (2025) to allow for the work in this area to be completed.

Figure 2. A–D) Removal of additional tailing from around the Carnegie Quarry during the 1930s. B) Explosives were used to remove large amounts of overburden from the stratigraphically top side of the quarry and were loaded into ore carts and then dumped into Neilson Gulch on the east side of the quarry (D). These tailing piles became the future parking lot for the Quarry Exhibit Hall, as seen in the recent photo (E, lower center) compared to an aerial photograph from the 1930s (F).

NPS

Paleontological monitoring work began in the QEH parking lot on September 10, after the overlying cap of asphalt was removed. In the first backhoe scoop into the underlying material, fragments of vertebrate fossils were found. On September 11, we discovered the first identifiable bone, a theropod vertebra, likely belonging to Allosaurus. The work thus continued, with daily smaller fossil discoveries being made as work took place through the historic tailings, as the crew excavated down to a depth of five feet throughout the parking lot area (Figure 3A).

As the work approached the anticipated area of the Quarry Sandstone, work slowed to allow for a more careful approach to this significant layer (Figure 3B). Vertebrate fossils were found on either side of the quarry sand, mostly comprised of smaller isolated sauropod vertebrae and rib fragments. While Rudolph and I were excited to be finding fossils, the construction crews were also excited, with many of their employees jumping in to try their hand at excavating and searching for fossils by hand rather than by backhoe alone.

As we worked closer to the Quarry Sandstone layer, we were able to isolate a more indurated and unexcavated area, to the point where it became a topographic high, a rather peninsula-like projection oriented east to west, in the middle of the otherwise excavated area (Figure 3C). We were able to get a full measurement on the thickness of this unit, as well as its unobscured dip, and collect samples from the top and bottom of the unit for Uranium/Lead (U/Pb) dating. To better document its total lithology, we were able to obtain a power washer, with one of the construction workers utilizing two days to clean a section of the layer.

Figure 3. A) Monitoring taking place in the Quarry Exhibit Hall parking lot. B) View of the Quarry Sandstone Layer as construction continued around the parking lot. C) View from behind the northeastern corner of the Quarry Exhibit Hall, looking to the southeast during construction. The Quarry Sandstone is visible to the left of the photo, parallel to the white truck.

NPS

Diplodocus Discovery

On September 16, after the washing was done, we were documenting the extent of the sandstone when I spotted a fossil bone in the cross section of sandstone (Figure 4A)! Upon further inspection it became clear that it was a large limb bone plunging down into the unit. Construction in this area of the parking lot was paused to allow Rudolph and me to assess and excavate this fossil.

After a week of excavating, we found a sauropod tail vertebra positioned over the long bone, which we now believed to be a sauropod tibia. Then we found a second vertebra, and then a third, all articulated (Figure 4B). Rudolph followed them to the east, and I worked to the west. All this excavation work took place while the parking lot construction still happened around us. While we were working down, the parking lot was beginning to rise up around us.

After they had excavated down five feet, the construction crew began the process of backfilling and laying down multiple sandwiched layers of fill and geotechnical fabric, to give strength and stability to the area for the next many decades of use. We had dump truck parades, full of fill material, in a constant procession alongside us, while compressors and steam rollers (also known as asphalt rollers or grade rollers) compacted the material around us. In a short amount of time, we were sitting in a deep trench surrounded by a fresh parking lot (Figure 4C).

Figure 4. A) ReBecca Hunt-Foster and the first Diplodocus bone, a tibia, discovered in the parking lot excavation. B) Rudolph Hummel with the first three articulated vertebra overlaying the tibia and fibula. C) The excavation quarry trench in the parking lot construction area, as viewed from behind the northeastern corner of the Quarry Exhibit Hall, looking to the southeast during construction. D) Quarry yoga in action with four UCC crew working around large field jackets.

NPS

The pit we dug was dominated by the main fossil field jackets of material we had uncovered in the center, bordered by long trenches, as we attempted to dig ever deeper to create a “mushroom” effect to isolate our fossil materials into manageable packages. This would often involve the need for extreme “quarry yoga” amongst our excavating staff, with people strewn horizontally, diagonally, and vertically throughout the trenches, and bent into wild pretzel-like shapes to remove the rock surrounding these fossils (Figure 4D).

These were tight areas bound by very hard sandstone on both sides. We were also anxious about digging too far outside of our discovery and potentially finding more fossils (a good thing for us; a bad thing for the construction deadline) or wasting time on non-fossiliferous and very hard sandstone that could be spent on more productive excavating.

As we continued to work towards the west, we found an additional six tail vertebrae in, articulated with the others, as well as an articulated radius and ulna (lower arm). By this time, we had been able to determine that this tail likely belonged to the long-necked sauropod dinosaur Diplodocus, which also happens to be the most abundant dinosaur found in the Carnegie Quarry. We also found several other isolated bones, a partial turtle, and abundant unionid clams, which are by far the most common fossil found in the Carnegie Quarry. Also surprisingly abundant were the remains of plants in the form of mostly carbonized wood, located directly under the specimen.

By September 26, we had come to the end of the tail, which we had been pursuing to the east. The vertebrae became smaller as we worked in this direction, and one day, nine tail vertebrae in, Rudolph found a distal tail vertebra that was missing its back half. It was cleanly sheared off and tilted upwards towards the surface of the former parking lot. We speculated that this most distal portion of the tail, if it had even been preserved at all, along with the proximal end of the original tibia we found, had probably been plowed off during the original road construction at the site in the late 1950s.

Several of these last vertebrae were in direct contact with the asphalt that would have been laid in the early 1960s during the first paving of the parking lot. Historic pictures of the grand opening of the Quarry Visitor Center on June 1, 1958, show that the parking lot still consisted of gravel and does not appear to have been paved until around 1959 (Figures 5A and 5B).

Figure 5. A & B) Quarry Visitor Center, June 1, 1958. C) Jacket removal, October 13, 2025; Cody Dickson (left); Hunt-Foster (right). D) Fossil jackets from parking lot excavation, October 17, 2025. Fossil extraction crew on fossil removal day. Front (from left to right): Hummel (DINO), Dickson (contractor), Robert Osteen (contractor), Hunt-Foster (DINO). Back: Duane Golden (left, DINO) and Devin Nelles (right, DINO). E) Fossils at Utah Field House of Natural History State Park Museum.

A & B) © 2023 Uintah County Regional History Center. C, D & E) NPS

As the discovery continued to grow in weight and length, the days we had available to work also began to decrease and get shorter. The excavation was still ongoing while the parking lot was finished up around us, but paving day was getting nearer, and every day we prolonged the work could end in great expense for both the construction contract and in delays in opening the area back to the public.

During excavation, we were able to get assistance from a host of volunteers, a Utah Conservation Crew (UCC), as well as some of our fellow DINO coworkers and the construction staff. This additional assistance was what was needed to help us get the jackets ready to be lifted out. On October 13, we removed the first small field jacket, containing a few of the vertebrae (Figure 5C). The weather began to change around this time, as we were met with several days of wind and rain, forcing us to work under impromptu tents made of tarps, ladders, poles and fence pickets across our excavation pit.

By October 17, we were ready to remove the remaining field jackets. The construction crew members were very helpful, providing the use of their skilled backhoe operator and machine to remove the large field jackets from the ground. The removal went well, with roughly 3,000 pounds of fossils and rock removed during the 2025 parking lot excavation (Figure 5D). Work is now underway to clean and study the remains, which are currently housed at the Utah Field House of Natural History State Park Museum in Vernal, Utah. The work can be viewed in the museum’s fossil preparation lab (Figure 5E).

Stay tuned for part two, which will discuss the continued excavation efforts in 2026 and additional discoveries.

References

Beidleman, R.G. 1964. Administrative history: Dinosaur National Monument. National Park Service Internal Report.

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

Carpenter, K. 2018. Rocky start of Dinosaur National Monument (USA), the world’s first dinosaur geoconservation site. Geoconservation Research 1(1): 1–20.

Carpenter, K., and L.H. Taylor. 2025. A river runs through it: The Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah. Geology of the Intermountain West 12: 25–74.

Rich, M.M., V.L. Santucci, and J.S. Tweet. 2025. The intersection of New Deal public works programs and National Park Service paleontology. New Mexico Museum of Natural History Bulletin 101: 409–423.

Tags: dinosaur national monument, fossils, paleontology, parkpaleonewsseries