By Christine Siddoway, professor of geology at Colorado College
Two overarching aspects define the geology of the Colorado Front Range*:
- a duality of crystalline and clastic rocks
- an enormity of scale of the geological structure that is the Range.
(*The Front Range is the name of the mountain range in which we reside. “Front” refers to the Rocky Mountain front.)
The duality of crystalline and clastic rock types is easy to discern, by anyone who takes in the western view from the Colorado College campus, or ventures out to study the lay of the land on foot, by bike, or in vehicle. The crystalline rocks are the granites and metamorphic rocks, made up of interlocking crystals of quartz, feldspar, and micas that hold up the high elevations, glacial cirques, and cliff-y escarpments in the range. The clastic rocks are the ones that form vertical spines and slabby stacks – often colorful or wonderfully weather-sculpted – that are emergent at the foothills – mountains transition. The crystalline rocks are a product of magmatism and melting, and the clastic rocks are a result of sedimentation, that is, the settling of fragments out of water and the sifting of particles out from wind to accumulate to great thicknesses over spans of geological time. Those processes have gone on for eons, and continue today. For those who get intrigued to know more of geology, there is a yet wider array of rock types to discover in Colorado, including the remains of carbonate platforms, volcanic fields, and seismic zones.
The enormity of scale is something that we can’t perceive all at once, but begin to understand gradually over time, and with deepening acquaintance. The bedrock and surface deposits that make up the Front Range formed over an immense span of time — that is one aspect of the enormity — and hold clues about the paleo-environments that existed in this place in the past. The records contained in the crystalline rocks go back nearly 1.8 billion years. Clastic rocks show upon the scene at approximately 750 million years ago, then there is a big gap with no geological record whatsoever, then reappear at 522 million years, with steady accumulation, more or less uninterrupted, until today. The other big aspect that we cannot directly see has to do with size.
View to West of the southern Front Range, from Palmer Park. From left to right, summits are Cheyenne Mountain, Mount Rosa, Almagre Mountain, and Pikes Peak. Crystalline rocks form the rock at high elevations, from cliff front to summits, and clastic rocks underlie the urban areas, Garden of the Gods, Red Rock Canyon park, and the gradual ramp that rises to the cliff break. Photo credit: Steve Weaver.
Profile View of the Geology in Colorado Springs
Profile view of the geology of Colorado Springs. People occupy and move around upon the thin line at the top of the diagram. A large number of geological formations ‘emerge’ in a narrow zone that corresponds to Garden of the Gods and Red Rocks Canyon city parks. Diagram is by Siddoway and Fitz Diaz, 2013.
This diagram is a geological cross section through Colorado Springs — a rendering of a vertical slice into the Earth that goes down just over 3 kilometers or 1.8 miles. The various geological formations are shown with different colors: pink for the crystalline rocks, and the stripe-y other colors for sedimentary rocks. A point equivalent to the place of contact between crystalline and clastic rocks in the mountains at the left side of the diagram would be found far below sea level at the right. What is this saying? The geology of the Colorado mountains is BIG, and fundamental to space, place, and our place in time.
The physical geography, active geological processes, and ecozones of Colorado have not always been the same as they are today. On these sites you can explore the paleogeography and paleoenvironments of Colorado, journeying through the past 550 million years via maps and videos of Colorado.
- Colorado Stratigraphy - (Dig into the stratigraphy of individual basins across the state using the basin map and stratigraphic chart)
- Denver Museum of Nature & Science
- Red Rock Canyon Open Space Geology
- Discovery of a carear - CC geology professor, Christine Siddoway helps tell a new story about the formation of the Front Range with discovery of old sandstone outcrops (700 million years older than previously thought!)
- CC Alum Discovery - (CC investigators were able to participate in paleontological excavations and paleoenvironment reconstruction of the Ice Age fossils.)