Vail Valley rocks tell tales of rising of the Rockies
Gore Range Natural Science School
Vail, CO Colorado
VAIL VALLEY, Colorado ” The first inklings of spring are beginning to peep out from the snowbanks and icy roads of Colorado’s Vail Valley and the Rocky Mountains.
We don’t see wildflowers yet. The first signs of spring in the mountains are mud and rocks and road cuts.
But it’s a geologist’s dream and I’m breathless over the chance to see Glenwood Canyon’s thick rich Mississippian limestones and the Minturn Formation’s beautiful shales and sandstones The melting snow reveals a world of history in the rock layers around us. We just need to learn a little of the language of geology to begin to understand the stories they have to tell.
Looking at the valley walls, you can’t help but notice the rich and varied colors and textures of the rocks that surround us. These colors and shapes tell us how rocks formed, helping us to understand the landscapes of the past.
Our valley is filled mostly with sedimentary rocks, which generally form when particles are deposited in water. Common sedimentary rocks in our area are easily distinguished and each provides insight into the environment in which they formed.
Gypsum, for example, easily identified by its white color and chalky texture, formed when sea water evaporated, leaving behind amorphous deposits that later oozed upward during periods of intense mountain-building. Dark gray shale that breaks easily into sheets or dull gray limestone layers tell the tale of deep water in a primordial sea and are often dotted with ancient marine fossils.
Grainy pink and red sandstones signify prehistoric beaches, where ocean waves crashed and river waters dropped sand-sized grains, cementing them together with minerals dissolved in the rushing waters.
Finally, unsorted, rounded rocks and conglomerates (mixtures of different sized particles) tell of prehistoric rivers with giant rapids rushing and rolling across the landscape. The Colorado landscape has changed many times over the eons, but each new transformation has etched its mark in creating the sweeping mountains and valleys that are our home.
Over the past 20,000 years or so, first glaciers, then rivers, carved out the Eagle River Valley, revealing rock layers that formed millions of years ago. The geological story of the Rocky Mountains essentially begins about 280 million years ago.
This area was covered by shallow seas and two massive mountain ranges, now known as the Ancestral Rockies, towered above the continent. The sea level in the large basin between the ranges moved up and down.
Our area was covered sometimes by deep oceans filled with plantlike animals whose fossils are now scattered throughout McCoy and Sweetwater in western Eagle County. At other times, this was an ancient beach, where rivers slowly wore down the mountains and carried them grain by grain to massive river deltas that deposited sand and silt, creating the red and peach sandstones that we see in Red Canyon.
At other times, this area was covered by rivers with fast moving rapids that deposited large, rounded particles, leaving us with conglomerates and unsorted rock deposits. We see some of these deposits in many places throughout the valley ” look for them near the Minturn entrance ramp to I-70, just across the river from the entrance to I-70 west.
After nearly 200 million years of depositing assorted sediments across the landscape, the shallow seas receded, leaving sedimentary rocks miles deep in its ancient seabed. The earth continued to change ” plates drifted and crashed. One such crash, approximately 70 million years ago, is believed to have begun the uplift (known as the Laramide Orogeny) that created the Rocky Mountains we see today.
While the formation of the Rocky Mountains is still a hotly debated topic in geologic circles, many geologists agree that the crash of the South American Plate into the North American Plate created a gradual crushing of the North American Plate that resulted in massive “wrinkles” that appeared in the western U.S.
The once flat, horizontal rock layers from the ancient sea were assaulted. Pushed from different directions, the rocks almost liquefied from the intense pressure and some changed from sedimentary rocks into metamorphic rocks such as quartzite, slate and marble.
The intense pressure also caused minerals to separate out from the rocks, forming the veins of silver, gold, and other precious minerals that are still mined in Colorado. Rocks were folded and bent, forming synclines (upward folds) and anticlines (downward folds) while some broke under the strain into huge fault blocks.
The evidence of this massive geological calamity is all around us. There are very few completely horizontal layers as we look around our valley ” most of the rocks have at least been tilted.
The layers turned vertical at the rest stop at Wilmore Lake just west of Edwards are part of a massive syncline, another clear piece of evidence of the tumult and chaos that must have accompanied this period of intense mountain building.
The geological story of the Rocky Mountains has many more chapters, including the tale of the Dotsero Volcano, the glaciers, and more, but one geology lesson a day is probably good for most people.
It seems that geology is often the most under-appreciated of the natural sciences. Rocks, usually buried in dirty mud, aren’t as exciting as wildflowers or wild animals. But only a small bit of knowledge is required to unravel yet another of nature’s mystery.
And let’s face it, rocks don’t run away or try to attack you ” you won’t get poisoned or poked from tasting or touching a rock, and you don’t have to worry about being accused of cruelty to rocks. So while you are waiting for mud season to end and summer playtime to begin, take a minute to appreciate the stories in stone that surround us.
Jaymee Squires is the graduate course instructor at the Gore Range Natural Science School. Gore Range Natural Science School’s “Nature Notes” will appear regularly in the Vail Daily. The Science School’s mission is to awaken a sense of wonder and inspire environmental stewardship through natural science education. For more information on upcoming programs and summer camps, visit http://www.gorerange.org or contact the school at 970-827-9725 x.10 or firstname.lastname@example.org.
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