Rocks common in Rockies |

Rocks common in Rockies

Tom Wiesen

To best answer this broad question, we look to the geologic rock record. Earth is believed to be 4.5 billion years old. What landscapes have covered our area over this unfathomable amount of time? Oceans, inland seas, mud flats, sand dunes, swamps, beaches, volcanoes, mountains and glaciers to name a few. Through plate tectonics, continents are slowly but continually propelled around the earth. The position of a continent on the globe affects the climate. There were times when this very ground we stand on was south of the equator, and the climate was tropical. At other times it was an arid desert covered by vast sand dunes much like the Sahara.Another time existed when the cool moist Colorado climate was ideal for giant redwoods to thrive. However, Colorado spent hundreds of millions of years quietly beneath the ocean accumulating sediments.The present day Rockies were berthed through violent earthquakes and volcanoes about 70 million years ago during an action-packed geologic period known as the Laramide Orogeny. Later, hot mineral rich solutions from deep within the earth pressured its way into the crannies and rock faults of Colorado, leaving a lacework of riches in gold and silver. Most of the landscape of our local mountains was formed through block faulting. Very large earthquakes caused giant blocks of earth to be drastically uplifted. It is this uplift that brings very old rocks from deep inside the earth to the surface where we can see them.Some of our landscapes in western Eagle County were formed by volcanic activity. Castle Peak, for instance, is a volcanic remnant. Also, as you drive over the Wolcott divide to State Bridge, you pass over an ancient volcanic rim. The most recent volcano in Colorado is located in Dotsero, and you can see the black lava rock near the log yards on the south side of I-70. In most recent geologic history, we emerged from the ice age a mere 10,000 years ago. For approximately 70,000 years the earth was colder overall and glacial ice covered our mountains. Our glaciers did not come from the north, but rather they grew from the mountaintops as alpine glaciers. Gravity pulled, and the heavy alpine glaciers gouged their way down high mountain valleys, plucking giant boulders from the landscape along the way, like a bulldozer of ice.About 10,000 years ago Earth’s climate warmed. We’re talking, “The Big Spring Runoff”. The melt water from the vast quantities of ice and snow caused huge floodwaters. Enormous rivers carrying huge rolling boulders and blocks of ice carved down through solid rock to form deep and spectacular canyons, and then later deposited a wealth of soils and gravels in the broad river valleys below.So to answer the question, “What formed this beautiful landscape?” The next time you look at sandstone cliffs, think of a beach or even sand dunes. When you see an arid landscape of shale, think of a deep ocean. Limestone boulders? Think of seashells. Eyeing a saw-toothed ridge on the skyline? Think glaciers. The ultimate answer is time has formed this landscape, and this landscape continues to evolve each day.Tom and Tanya Wiesen are the owners of Trailwise Guides. Daily private outings and instruction are available for wilderness hiking, backcountry mountain biking, bird watching and natural history tours. Call Trailwise Guides at (970) 827-5363.Vail, Colorado

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