Paleontology of Morrison–Golden Fossil Areas National Natural Landmark

Article by Justin Tweet, NPS Paleontology Program

Morrison and Golden, Colorado, west-southwest of Denver, are just east of the steep rise of the Rocky Mountains. Ridges of tilted rocks in these cities herald the mountains looming to the west, and crossing many tens of millions of years of geologic time can be done in a short walk. Here is a concentration of Mesozoic fossil sites spanning from the Late Jurassic to the end of the Cretaceous, about 150 to 66 million years ago, showing changes in land animals over time. The significant paleontological heritage of this area has been recognized as Morrison–Golden Fossil Areas National Natural Landmark (NNL).

A view of the tracks exposed at Dinosaur Ridge, one of the components of Morrison–Golden Fossil Areas National Natural Landmark. The tracks are dark due to an application of charcoal dust.

Photo courtesy of Dinosaur Ridge/Amy Atwater

Morrison–Golden Fossil Areas NNL includes five tracts: an area in Morrison including a fossil quarry in the Late Jurassic Morrison Formation developed by Arthur Lakes in the 1870s; Dinosaur Ridge, famous for its dinosaur tracks from the beginning of the Late Cretaceous; and three tracts in the Golden Fossil Area (North Golden or Early Bird, Triceratops Trail, and School of Mines).

A map of the components of Morrison–Golden Fossil Areas NNL, with significant discoveries highlighted. From north to south the five components are North of Golden, Colorado School of Mines, Triceratops Trail, and Dinosaur Ridge East Side and West Side (including the Morrison quarries).

Map by Martin Lockley, courtesy of Dinosaur Ridge/Amy Atwater

The Morrison quarries are the source of the first fossils of the great Late Jurassic dinosaurs of North America that were brought to the attention of scientists. In 1876, Arthur Lakes, a professor at what is now known as the Colorado School of Mines in Golden, began corresponding with paleontologist O.C. Marsh of Yale about fossil discoveries. By the end of 1877, quarries opened by Lakes in Morrison had supplied the first fossils of famous dinosaurs such as Apatosaurus and Stegosaurus. These fossils were part of the "Bone Wars" between Marsh and Edward Drinker Cope; Lakes corresponded with both scientists, but in the end the fossils went to Marsh. The quarries were only worked for a short time, and the locations of some of them were lost, but they have been relocated in recent decades and new fossil discoveries have been made at these historic localities.

The type or name-bearing specimen of Apatosaurus ajax, from Quarry 10, as illustrated by O.C. Marsh (first use in 1879, Plate VI of “Principal Characters of American Jurassic Dinosaurs: Part II”, American Journal of Science XVII: 86–92.).

American Journal of Science

The most famous part of Morrison–Golden Fossil Areas NNL is Dinosaur Ridge. Although there are dinosaur bones and "brontosaur bulges" (sauropod tracks) in the Morrison Formation on the west side of the ridge, Dinosaur Ridge is best known for the fossil track beds exposed on the east side. Here, dinosaur footprints and other trace fossils from the earliest Late Cretaceous (about 100 million years ago) can be seen. They were first exposed in 1937 by blasting for the Alameda Parkway to Red Rocks Park (itself now a National Historic Landmark), and are just above the road, on the light-colored rock faces sloping toward it. The original exposures have been joined by additional fossil trackways revealed by excavation in 1992. Preservation and protection here are complicated: the thin track-bearing beds dip steeply and have little natural support to keep them from breaking loose and sliding down, or to keep overlying beds from sliding down on them.

This view of the track surface shows support structures used to prevent overlying beds from sliding onto the track-bearing surface. Tracks are less apparent in this photo because they are not highlighted by charcoal dust, but some are visible.

Photo courtesy of National Natural Landmarks Program/Deborah DiQuinzio

Geologically speaking, the tracks are found in the upper part of the Dakota Group, deposited in the early Late Cretaceous. At this time, a vast shallow seaway was advancing across the interior of North America, which was much lower in elevation (the Rocky Mountains did not exist yet). The future South Platte Formation was a sandy coastal strip next to the sea on the east and was used for north-south travel by dinosaurs and other vertebrates. So many fossil tracks have been found in it and equivalent rocks that they are called a "dinosaur freeway". The kinds of tracks found here mostly belong to three-toed (tridactyl) dinosaurs. Most were made by hadrosaur ornithopods, early cousins of the "duck-billed" hadrosaurids from later in the Cretaceous. The trackmakers were probably similar to Eolambia. Juvenile and adult tracks are known for these dinosaurs. More slender three-toed tracks were made by theropods (the group including birds), among them ostrich-mimics. Two kinds of fossil tracks were named from specimens found in these rocks, the theropod track Magnoavipes caneeri and the ornithopod track Caririchnium leonardii. Invertebrate traces and evidence of microbial mats have also been found. Slightly older Dakota Group tracks from Dinosaur Ridge include two-toed tracks of dromaeosaurs.

Several large and small Caririchnium tracks can be seen here highlighted by charcoal dust. Dust washes out over time and is reapplied.

Photo courtesy of Dinosaur Ridge/Amy Atwater

More Dakota Group tracks are found on rock faces on a ridge at the North Golden tract, including the examples used to name the crocodilian track Mehliella jeffersoni and the bird track Ignotornis mcconnelli. These fossil tracks were described in 1931, but the discovery site was not recorded in detail and was only relocated recently.

The geologically youngest parts of Morrison–Golden Fossil Areas NNL are the Colorado School of Mines tract and Triceratops Trail. Both of these tracts are located within Golden in the Laramie Formation, which was deposited on a coastal plain shortly before the end of the Cretaceous. Both have abundant tracks of dinosaurs and other animals, as well as plant fossils. Unlike the typical fossil site, Triceratops Trail is located within a golf course. The fossils here were first discovered when the area was used as a clay quarry. After quarrying operations ended and work began for the golf course, some of the land was used to preserve the fossils.

A preserved track-bearing surface on the Triceratops Trail, part of a former clay quarry.

Photo courtesy of Dinosaur Ridge/Amy Atwater

This site has several unusual and notable kinds of track, including the specimens used to name the champsosaur (unarmored crocodile-like aquatic reptile) track Champsosaurichnus parfeti, the horned dinosaur track Ceratopsipes goldensis (likely made by Triceratops), and the tracks of a small hopping mammal, named Schadipes crypticus. The horned dinosaur tracks are notable because such tracks are extremely rare, despite the abundance of body fossils. Hadrosaurid tracks, rare theropod tracks, bird tracks, and palm fronds and other plant fossils are also found here. One particularly large three-toed track was thought to possibly be a tyrannosaur track, but is now considered to be a hadrosaurid track. Tracks are seen on steeply tilted sandstone "fins", reoriented from horizontal by the Golden Fault.

A Ceratopsipes goldensis track at Triceratops Trail, likely left by Triceratops.

Photo courtesy of Dinosaur Ridge/Amy Atwater

With so many different fossil localities, the history of Morrison–Golden Fossil Areas NNL is complex. The Morrison quarry and Dinosaur Ridge tracts were designated as Morrison Fossil Area NNL on November 7, 1973, but protection of the sites was not organized until the late 1980s. Friends of Dinosaur Ridge was established in 1989 with a focus on Dinosaur Ridge, but expanded operations to the north to support what is now known as Triceratops Trail, with the trail being completed in 2004. The three Golden-area tracts were added to the NNL in 2011 and the name was changed to Morrison–Golden Fossil Areas NNL.

Administered by the National Park Service, the National Natural Landmarks Program recognizes and supports the voluntary conservation of exemplary biological and geological sites that illustrate the nation’s natural heritage, including those that contain significant paleontological resources. National natural landmarks are designated by the Secretary of the Interior and are owned by a variety of public and private stewards. To date, significant paleontological resources have contributed, in whole or in part, to the designation of 58 National Natural Landmark sites across the country, and paleontological resources are known at many others as well. These landmarks represent the range of geologic history from very early marine life 510 million years ago to more recent (40,000 years ago) fossil mammals.

Morrison–Golden Fossil Areas NNL is one of 58 National Natural Landmarks designated primarily for paleontological resources.

Photo courtesy of Dinosaur Ridge/Amy Atwater

Most NNLs have a plaque similar to the one installed at Dinosaur Ridge that display the site name, establishment date, and brief description of the designation. The text on the Dinosuar Ridge plaque reads:

Morrison Fossil Area
has been designated a
National Natural Landmark
This site possesses exceptional value
as an illustration of the nation's natural
heritage and contributes to a better
understanding of the environment
1975
National Park Service
United States Department of the Interior