If These Rocks Could Talk…
Jeff Mitton
Natural Selections (Published December 9, 2005, in the Daily Camera)
Continents converged in a slow-motion collision, and the land buckled. Mountains rose out of a shallow sea. It was the beginning of the Flatirons.
Approximately 315 million years ago (mya), the continents of North America, South America, and Africa drifted together to create the supercontinent called Pangea. All of the land masses, including Australia, Eurasia, and Antarctica, were united. At that time, the land that would later be called Colorado was south of the equator.
When the continents collided, the Ancestral Rockies rose, with the Ancestral Front Range rose close to the position of the modern Front Range. Rivers and streams drained to the sea, just east of Boulder. The mountains must have been high and steep, for the streams washed stones, rocks, and boulders from the canyons and deposited them between the mountains and the sea. The loose mudstone, sandstone, and conglomerate lithified, or solidified into stone. This layer of stone, more than 1,000 feet thick in places, is the Fountain Formation. It is named for Fountain Creek, which flows through Manitou Springs and Colorado Springs. The Fountain Formation has been sculpted into the Flatirons in Boulder, Red Rocks near Morrison, and Garden of the Gods in Colorado Springs.
About 300 mya, wind-blown sand piled up near the town of Lyons, and it solidified into the Lyons Formation. Assembled by wind, rather than water, Lyons sandstone is not as strong as the Fountain Formation, but it has attractive colors, and it splits nicely into blocks. The buildings at CU are faced with Lyons sandstone.
The Fountain Formation was deposited by powerful rivers, and it was buried relatively quickly. Over many millions of years, chemical processes modified the Fountain Formation in Boulder in a distinctive way. Iron-bearing minerals, biotite and hornblende, were transformed into hematite, which gives the local sandstone its distinctive hue and hardness.
The modern Rocky Mountains began to rise 65 mya, when eastern Colorado was beneath the Cretaceous Interior Seaway. So the young Flatirons clung to the mountains at the edge of the sea. At the same time, a large comet slammed into the Yucatan, triggering a nuclear winter, and causing the extinction of the dinosaurs.
The thrust of the mountains was extreme here, tilting the Fountain Formation more than 50 degrees; the angle of tilt at Lyons is only 20 degrees. The extreme uplift and the unusual hardness of the local Foundation Formation combined to produce the Flatirons. Their extreme hardness makes the Flatirons ideal for climbing, and also allows the Flatirons to resist the forces that erode softer stone.
Early settlers cut some of the local Fountain Formation into slabs for sidewalks. Biologists noted that some of the slabs had the fossilized tracks of an amphibian, Brachydactylopus fontis. The tracks were formed 300 mya, before the dinosaurs evolved. One of these sidewalk slabs can be seen at the University Museum. Our local Fountain Formation is otherwise lacking in fossils, but marine fossils are in the Fountain Formation near Castle Rock.
When local residents resolved to build a University, they began to quarry the Fountain Formation, at the base of the Flatirons. But the good folks of Boulder realized that the quarry would ruin their beautiful Flatirons, so they bought out the quarry. That purchase, inspired by esthetic values, was the beginning of our Mountain Park.
The Flatirons are like the open pages of a book, read most avidly by geologists. The Fountain Formation began to form as Pangea was welded together, and the Ancestral Rockies began to erode. The Flatirons were lifting up just as the dinosaurs went extinct. Thus, the formation of the Fountain Formation and the rise of the Flatirons mark two momentous events in geology and evolution.