The Friends of the Florissant Fossil Beds

Towards the end of the summer, Dr. Herb Meyer took our paleontology interns, Kathy Salas and Eva Lyon, and myself on a tour of part of the Gold Belt Byway. The Gold Belt Byway is a National Scene Byway which winds through spectacular scenery and includes 21 stops of historic or scientific importance, including Florissant Fossil Beds National Monument, the Cripple Creek Mining District, the rich dinosaur fossil sites of Garden Park, and an important Ordovician trace fossil site at Indian Springs Ranch.

Earlier this summer during seasonal training, we visited several of the stops in the Florissant area (Stops 2, 3, 5; the park’s visitor center and petrified forest are Stop 1). If you want to take the Gold Belt Byway Tour yourself, Geologic Guidebook to the Gold Belt Byway, Colorado, co-authored by Meyer and 4 other geoscientists, is a beautifully illustrated self-guide to the 21 stops and a great introduction to local geology and paleontology.

Last Friday, we visited several additional stops, in reverse order to the Geologic Guidebook. We began with a stop overlooking Dome Rock (Stop 4), an exfoliation dome of 1.07-billion-year-old Pikes Peak Granite. Exfoliation domes form in some granites by the processes of chemical and physical weathering, particularly the action of ice.

At left, you can see a dramatic example of the difference between ecosystems on north and south-facing slopes in the Rocky Mountains. This is because south-facing slopes receive significantly more sun and are warmer and drier. North-facing slopes are moister and colder. After driving through Cripple Creek, we took the scenic Shelf Road to Cañon City.

The Shelf Road (Stop 18) continues through 1.7-billion-year-old granodiorite, considerably older than the Pikes Peak and Cripple Creek Granites. Unlike the Pikes Peak Granite, this granodiorite tends to weather linearly rather than producing exfoliation domes. Sometimes this weathering produces natural arches, like the one at right.

Near the end of the Shelf Road, you can see a contact betweeen the 1.7-billion-year-old granodiorite and the Ordovician Manitou Dolostone (more commonly called the Manitou Limestone). This gap of missing time in the rock record–about 1.2 billion years–is what geologists call a noncomformity. The Manitou Limestone, Harding Formation, and Fremont Dolostone span the time period of about 500 to 439 million years ago. All contain marine fossils such as brachiopods, clams, trilobites, snails, armored fish (ostracoderms), corals, algal mounds (stromatolites), and nautiloids.

We then met Melissa Smeins from the Bureau of Land Management in Cañon City and her intern, Charlie Bondy. Bondy has been working on an educational tour of the area which overlaps partially with the Gold Belt Byway Tour, and she led the next part of the tour, through Red Rock Canyon State Park, the Garden Park Fossil Area, and Skyline Drive. Red Rock Canyon State Park (Stop 17) exhibits excellent outcrops of the Pennsylvanian Fountain Formation (deposited 296-290 million years ago). The Fountain is composed of sandstones and conglomerates, and represents an ancient alluvial fan deposited by rivers entering a shallow continental ocean.

At left, you can see crossbedding created by sediments deposited on the trailing edges of sand and gravel bads. Crossbedding indicates deposition in moving water, and is one piece of evidence for the Fountain Formation being an alluvial fan deposit. The large size of many of its clasts (component pebbles and cobbles) also indicates that the sediment did not travel far from its source–in this case the Ancestral Rocky Mountains. Only a few fossils have been found in the Fountain Formation, due to its coarseness, but these are important for reconstructing the paleoenvironment. These fossils include tracks of an extinct amphibian, marine fossils, and some early plants, such as “scale trees” (tree-sized relatives of modern clubmosses), tree-sized horsetails, and seed ferns.

Next we continued to the historically and paleontologically important Garden Park Fossil Area, where Bondy interpreted the history of the area for us.

-Melissa Barton

Photo Credits: Melissa Barton

Geologic Guidebook to the Gold Belt Byway, Colorado, by Thomas W. Henry, Emmett Evanoff, Daniel A. Grenard, Herbert W. Meyer, and David M. Vardiman (Gold Belt Tour Scenic and Historic Byway Association, 2004), is available at the Florissant Fossil Beds National Monument Visitor Center for $19.95 plus tax.

More Gold Belt Byway Posts:

• Stops 1, 2, 3, 5: Seasonal Training Field Trip (Florissant Area)
• Stops 12, 14, 15, 16: Garden Park and Skyline Drive Fossil Sites
• Stops 19, 20, 21: Indian Springs Trace Fossil Site and Phantom Canyon