The Broomcorn Express, Quarterly Publication of the Broomfield Historical Society
Vol. 5, No. 1, June 2025
So you walk the path that once was trod
By wise and ancient kings
Searching in the mists of time
For gifts of unknown things
— From Gifts of Unknown Things by Jim Capaldi
INTRODUCTION
It’s not that I think we have completely covered all aspects of Broomfield’s relatively recent history, but I thought it might be interesting for a change to set the wayback machine to an even earlier time and try to tell a part of the pre-human history story of our area. You may have seen the news reports in the past year of a group of high school students looking for and finding dinosaur remains on the north side of Broomfield.1 What you may not be aware of is that Colorado has more fossil sites than any other state. It is important to understand why we need to dig into the history of the area by learning about its evolution through geological time that created the environments necessary for fossil preservation.2 The who, what, when, where and why of the fossil record may not be generally known but they form an important piece of Broomfield history.
THE GEOLOGY OF BROOMFIELD
Dinosaur fossils are intimately linked with the history of the rock layers they are associated with. This online geological map of the Front Range includes Denver and stretches north.3 Although it lacks much cultural information, Standley Lake is labeled and easily identifiable. To the northeast, the next lake is the Great Western Reservoir—so we have a known point that is on the west side of Broomfield. If you draw a horizontal line due east from the top of the reservoir to the S curve in the South Platte River, you are generally following Highway 128 and 120th Avenue across Broomfield.
Triceratops reconstruction at Dinosaur Ridge (photo by author).
The colors on the map represent the different ages of rocks- tans and pinkish colors are very recent Pleistocene layers of loess and alluvium that represent erosion of previous rock layers during ice age glaciation resulting in fine grain unconsolidated soils with numerous cobbles. Interspersed with those areas we see pockets of green: these are much older Cretaceous rocks (going from older to younger) of the Laramie, Arapahoe, and the Denver Formations. These rock outcrops are important here because most of the dinosaur tracks and fossils found in Broomfield and surrounding counties come specifically from these rock layers.4 The Cretaceous rocks of interest here were deposited between 69 and 65.5 million years before the present.
Rocks in the Laramie Formation are primarily made up of sandstone, mudstone, and clay5; the Arapahoe Formation consists of conglomerate, sandstone, and claystone; and the Denver Formation is made up of shale, claystone, and sandstone.6 The point here is that while these rock layers were deposited in adjoining time slices, their composition is very different, which implies that they were deposited in different environments—which may be significant in terms of the types of fossils that they may contain.
THE CRETACEOUS ENVIRONMENT: LAND, PLANTS, AND ANIMALS
As you may be aware, there is evidence that over geological time, continents can move creating new oceans and potentially colliding to form new continents and drive-up mountain ranges. At the start of the Cretaceous, much of today’s Colorado was under water: an ocean called the Western Interior Seaway ran from the North Pole to the Gulf of Mexico. Over time the water level in the seaway receded and “the sludgy sediment left behind was ideal for capturing the animals and plants that flourished in the subtropical climate.”7 Consider the implications: if you lived in what will become the Anthem or Baseline communities during the Cretaceous, you might be under water from an inland ocean. If you head west to Skyestone, you are not just on land but heading towards rugged mountains. In between near Arista there is a pre-historic natural equivalent of I-25: a sandy beach running for hundreds of miles going north and south that creates a natural migration path for the animals of the time. Sometimes the beach is interrupted by rivers flowing out of the mountains that are surrounded by low-lying swampy areas, all basking in a climate more like today’s Houston than Broomfield.
Why tell you about paleo environments when the idea was to talk about dinosaurs? A paper by Carpenter and Young makes the case that the assemblages of dinosaurs varied by the environments that they lived in.8 They characterize the Laramie Formation as being associated more with swampy and near-river locations that had a varied faunal assemblage including Tyrannosaurus and Triceratops. Laramie flora includes myrtles, figs, and an extinct genus of palms.9 The Arapahoe Formation is characterized as a conglomerate, with its composite materials derived from nearby mountains, making it of more terrestrial origin; it has yielded comparatively few fossils, mostly from ceratopsids. Plants associated with the Arapahoe are essentially the same fauna as in the Denver Formation and include maples, birches, oaks among others.10 The Denver Formation differs from the other two yet again and may be an intermediate environment that has a varied dinosaur assemblage including Tyrannosaurus, Triceratops, and hadrosaurids. It’s probably an appropriate time to mention that the rocks from the Cretaceous would lead you to believe that Broomfield was a dinosaur wonderland, but by the end of the Cretaceous, dinosaurs had become extinct. Moreover, although many of their fossils have been found, most represent scattered fragments as opposed to recognizable skeletons, which “suggests a considerable passage of time between death and burial of the specimens.”11
Fossils and casts from the Denver Formation collected in Broomfield in 1997.19
THE FOSSIL RECORD
Having thought about the rocks beneath our feet, their age, the environments that they were deposited in, and the animals and plants that they are associated with, we need to understand the support for the idea that dinosaurs once lived here. Specifically, what could possibly remain of animals and plants that died millions of years ago? Fossils are anything that is preserved when time, heat, and pressure turn a layer of the earth from soft sediments into hardened rock layers. Along the way, bones and components of the skeleton of an animal can be replaced by minerals, thereby preserving their original shape. As it turns out, there are different mechanisms that may preserve other evidence of earlier life: footprints, trackways, exoskeletons, shells, the outline and internal structure of plants, and petrified wood are all examples of fossils.
If you need a deeper dive into the fossils of our area, consider a day trip to Dinosaur Ridge in Morrison. Dinosaur Ridge is considered the best site to accessibly see long tracks of multiple types of dinosaurs, while their small exhibit hall has a series of maps and dinosaur assemblage pictures that will let you get up close and personal with the world as it may have looked in the Late Cretaceous.12 You can also take in Triceratops Trail in Golden which is the #3 track site in the US,13 where you can not only see Triceratops, Tyrannosaurus, and duck-billed dinosaur footprints, but also rain drops, palm frond impressions, and insect tracks captured in stone which gives some sense of the diversity of fossil evidence that remains.
Something you can do right now is take a trip to the Broomfield Library. In the entry atrium, just past the side door to the auditorium, is a slab of rock that was identified in 1999 in landscaping in the Interlocken Business Park close to the Rocky Mountain Metropolitan Airport. Based on the descriptive information in front of the rock slab, 23 tracks are visible, and they are attributed to both bird-footed ornithomid and mammal-footed theropod dinosaurs.14 The material near the tracks says the rock is from the Laramie Formation: given the identification of clear three-toed footprints from a bipedal ornithomimid dinosaur, it seems like the slab is more likely to be from the Denver Formation. (The type species of Ornithomimus velox was first discovered in 1890 in Colorado. It is believed to have been covered in feathers and had a toothless beak.15) This is probably a good place to point out that fossil identification can be challenging for several reasons, including incomplete primary preservation, incorrect geological formation attribution, broken or fragmented remains, erosional effects, and transportation of fossils to a different location. The Wright and Lockey (2001) article that was used to extract the information on display at the library about the trackways says that when they examined the slab it had already been moved and the outcrop from which it came was unknown and no longer exposed, which clearly adds some uncertainty about age determination. Within the next year, there is a plan to move the library rock slab to CU Boulder, where I’m sure the paleontologists will work to establish the correct age and fossil identification; in the meanwhile, visit and do your own investigation.
Tracks of a small ornithomid dinosaur in the Broomfield Library (photo by author).
PEOPLE AND FOSSILS
The first indigenous people on the continent are thought to have arrived about 12,000 years ago, which means that a mere 64+ million years separated them from our late Cretaceous dinosaurs. The layers of rock with fossils will have been buried, uplifted, and eroded in the intervening time, which means that just like today, it is entirely possible that the earliest residents of Colorado could have found fossils, and we can surmise that they would have easily recognized bones that were unlike those from animals they hunted. In one article, I found the following insights: “rock art and oral traditions centering on winged monsters and giant, primal beasts suggest that Native Americans across the West found remains and explained them, often via creation stories, over thousands of years. Navajo elders in the 1930s, Mayor writes, spoke of “places in the desert where one could see monstrous heads ‘sticking out from roots of trees and stones, from springs and swamps.’ ”16 The start of scientific paleontology in Colorado dates back to the 1860s, and by the 1870s, excavations had started at locations like Dinosaur Ridge. Modern construction continues to unearth fossils around the Front Range, such as the Interlocken slab.
FOSSIL-RELATED LAW
If you feel energized to go out and do your own fossil-related exploration and collection, it’s probably worthwhile to mention that there are laws you should be aware of. If you are on Federal land, you can’t collect fossils from vertebrates due to restrictions from the Paleontological Resources Preservation Act. You can collect invertebrate fossils for yourself but can’t sell them. The rules for collecting fossils in National Forrest System lands are governed by the same laws.
Collecting fossils on Colorado state-owned lands also has restrictions and permitting requirements, as well as associated special requirements on extraction of the fossils.17 Vertebrate fossils are considered public property and are sent to museums and universities.
If you are on private land, obviously you should first have the landowner’s permission to be there. If it is your property or you have permission to be on someone else’s property, you can collect and keep or sell any fossils you find.18
Perhaps the best general guidance is this: if you do happen to find a significant fossil anywhere, leave it undisturbed, take pictures, note the location, and forward the information on to one of our local museums to assess its relevance.
The county government of Broomfield itself would not normally be a repository for fossils. However, through an unusual chain of custody, it received a collection of fossils and casts collected in Broomfield in 1997, which currently resides in our archives. The CCoB received the necessary permit to retain those materials locally, which appear in the photo on the previous page.19
AFTERWORD
I wrote this article after seeing the news reports of fossils being found by high school students in Broomfield and wondering how they might be retained and displayed for the greater Broomfield population. In addition, I spent some time looking at the slab in the Broomfield library and wondered about how you could put something in plain sight and still have people walk by without noticing something so significant.
If you feel motivated to find out more, here are two books you can use as references. The first is Walking With Dinosaurs by Anthony Fredericks, which tells you about fossil sites throughout Colorado, with instructions on how to get there and what to look for.20 The other is Geology Underfoot Along Colorado’s Front Range by Lon Abbott and Terri Cook, which will fill in the details on local geology and has information on the best sites to visit.21
Finally, a few local (but out of county) field trips can give you a sense of what looking for fossil evidence in the field involves: Dinosaur Ridge in Morrison and Triceratops Trail in Golden are both mostly accessible sites to view in situ dinosaur tracks and are an easy day trip from Broomfield.
1. Hernandez, Elizabeth, and Elizabeth Hernandez. “Dinosaur Footprints, Fossils Discovered “in Our Own Backyard” in Broomfield.” The Denver Post, June 2, 2024. https://www.denverpost.com/2024/06/01/dinosaur-fossil-footprints-broomfield/.
2. Fredericks, Anthony D. Walking With Dinosaurs: Rediscovering Colorado’s Prehistoric Beasts. Boulder, CO: Johnson Books, 2012.
3. Trimble, Donald E., and Michael N. Machette. “Geologic Map of the Greater Denver Area, Front Range Urban Corridor, Colorado.” Accessed February 7, 2025. https://doi.org/10.3133/i856h.
4. Carpenter, Kenneth, and D. Bruce Young. “Late Cretaceous Dinosaurs From the Denver Basin, Colorado.” Rocky Mountain Geology v. 37, no. 2 (November 2002): 237–54. https://www.researchgate.net/profile/Kenneth-Carpenter-2/publication/40662150_Late_Cretaceous_dinosaurs_from_the_Denver_Basin_Colorado/links/58c6e470a6fdccde55e3ae92/Late-Cretaceous-dinosaurs-from-the-Denver-Basin-Colorado.pdf.
5. Wikipedia contributors. “Laramie Formation.” Wikipedia, December 1, 2024. https://en.wikipedia.org/wiki/Laramie_Formation
6. Wikipedia contributors. “Arapahoe Formation.” Wikipedia, January 3, 2021. https://en.wikipedia.org/wiki/Arapahoe_Formation.
7. LaRusso, Jessica. “A Dinosaur Lover’s Guide to Colorado.” 5280, July 1, 2023. https://www.5280.com/a-dinosaur-lovers-guide-to-colorado/.
8. Johnson, J Harlan. “The Paleontology of the Denver Quadrangle, Colorado.” Accessed February 8, 2025. https://coloscisoc.org/wp-content/uploads/2020/07/CSS_Proc_v12_pp369-378_Paleontology_Denver_Quad-JHJohnson-pt2.pdf.
9. Wikipedia contributors. “Laramie Formation.” Wikipedia, December 1, 2024. https://en.wikipedia.org/wiki/Laramie_Formation.
10. Johnson, J Harlan. “The Paleontology of the Denver Quadrangle, Colorado.” Accessed February 8, 2025. https://coloscisoc.org/wp-content/uploads/2020/07/CSS_Proc_v12_pp369-378_Paleontology_Denver_Quad-JHJohnson-pt2.pdf.
11. Johnson, J Harlan. “The Paleontology of the Denver Quadrangle, Colorado.” Accessed February 8, 2025. https://coloscisoc.org/wp-content/uploads/2020/07/CSS_Proc_v12_pp369-378_Paleontology_Denver_Quad-JHJohnson-pt2.pdf.
12. Ruiz, Elizabeth. “Denver 7 Colorado News (KMGH).” Denver 7 Colorado News (KMGH), August 30, 2019. https://www.denver7.com/news/political/national/dinosaur-ridge-in-colorado-ranked-no-1-track-site-in-all-of-u-s.
13. Lahale, and Lahale. “Triceratops Trail: An Easy Colorado Hike in the Tracks of Dinosaurs | Family Well Traveled.” Family Well Traveled | Family Travel Blog Offering Encouragement and Tips for Easy and Affordable Travel With Kids, October 25, 2024. https://familywelltraveled.com/2019/08/31/triceratops-trail-an-easy-colorado-hike-in-the-tracks-of-dinosaurs/.
14. Wright, Joanna, and Martin Lockley. “Dinosaur and Turtle Tracks From the Laramie/Arapahoe Formations (Upper Cretaceous), Near Denver, Colorado, USA.” Cretaceous Research 22, no. 3 (June 1, 2001): 365–76. https://doi.org/10.1006/cres.2001.0262.
15.Wikipedia contributors. “Ornithomimus.” Wikipedia, October 26, 2024. https://en.wikipedia.org/wiki/Ornithomimus.
16. LaRusso, Jessica. “A Dinosaur Lover’s Guide to Colorado.” 5280, July 1, 2023. https://www.5280.com/a-dinosaur-lovers-guide-to-colorado/.
17. “Archaeology & Paleontology Permits | History Colorado,” n.d. https://www.historycolorado.org/archaeology-paleontology-permits.
18. Ancient Odysseys. “Can I Keep Fossils I Find? Understanding the Laws Around Fossil Collection,” May 21, 2024. https://www.ancientodysseys.com/post/can-i-keep-fossils-i-find-understanding-the-laws-around-fossil-collection.
19. CatalogIt. “CatalogIt HUB,” n.d. https://hub.catalogit.app/9352/folder/entry/39306730-47f0-11ed-bbc8-4585eef376c9.
20. Fredericks, Anthony D. Walking With Dinosaurs: Rediscovering Colorado’s Prehistoric Beasts. Boulder, CO: Johnson Books, 2012.
21. Abbott, Lon, and Terri Cook. Geology Underfoot Along Colorado’s Front Range. Geology Underfoot, 2012.