Fossils in Cañon City Fountain Conglomerate
by Cindy Smith
The Pennsylvanian Fountain Formation in Cañon City has long been prized for quarrying, as it contains an unusual highly-cemented conglomerate that has been used in the building stone of at least two buildings: 8 columns in the East Lobby of the US Capitol in Washington DC, and polished interior and unpolished exterior facing slabs in the Fremont County Administrative Building (FCAB) in Cañon City. This striking conglomerate takes a beautiful polish.
The Crossroads Through Time Steering Committee members have been doing extensive research on the quarry that produced this conglomerate trying to determine ownership when it was a working quarry and locating buildings where it was installed, as we are hoping to receive a large block for our Crossroads Through Time – Geology Time Trail, where it would be placed at the 310 million year mark. Recently our research took an unexpected turn.
Crinoids! Our local Pueblo Community College-Fremont Campus geology instructor Paul Denney discovered large numbers of these fossils in the conglomerate. During a ‘field trip’ to look at the conglomerate interior walls of the FCAB, we found beautifully shaped crinoid columnals, many star-shaped, plus one unexpected collection of distinct crinoid arms with pinnules. The mind boggles at how this collection of delicate arms managed to remain intact while being beaten about by 1-4″ chunks of rock in a thrashing streambed.
Dr. Gary Webster of Washington State University, now 84, wrote his graduate thesis on mapping the Royal Gorge Quadrangle for the University of Kansas, as well as a paper on the geology of the Twin Mountain area in Cañon City where the conglomerate was quarried. WIPS member Jim Nelson located and contacted Gary, who kindly offered his help and thought he might be able to identify and thus date the conglomerate if we could find crinoid calyces. Unfortunately we couldn’t.
Dr. Webster believes most of the crinoid pieces come from the Order Cladida, a dominant crinoid group in the Permian and Pennsylvanian. He suspects they are from the Minturn Formation, Atokan-Desmoinesian Age (307-315 million years old). But one columnal with 5 accessory canals may be a Devonian gasterocomid crinoid, with surrounding clasts from the Broken Rib Member of the Dyer Formation; this group is thought to have become extinct in the Late Mississippian. With further research, we’ve learned that the source of the basal Fountain in the Cañon City area came from the northwest, not from the northeast as we had assumed. Clearly we have more research to do to clarify and identify the age of the Cañon City area Fountain conglomerate.
We are now digging deeper into crinoid anatomy and terminology, a delightful by-product of our original goal of ‘simply’ moving a multi-ton block of conglomerate to the Geology Time Trail. Dennis Gertenbach has helped us understand the phylogeny and morphology of these creatures. Often for me, it’s the lure of the forensics, the not-knowing-where-this-will-lead aspect in paleontology that fascinates and pulls me in.
As an aside, our County Commissioners were a bit puzzled and guarded to find five of us with our loupes and noses pressed to the polished walls outside their meeting room. They apparently didn’t get the notice that we would be out scouting. Once introduced to crinoids, they relaxed, smiled, and received their introduction to the world of Deep Time.