Generally speaking, our local mountains were formed through block faulting about 70 million years ago. Large blocks of the earth’s crust were thrust upward during a long and intense period of earthquakes. To this day, a doozey of an earthquake occurs in Colorado about every 60,000 years.
These large landmasses were thrust skyward and left to the elements of erosion. Ancient rock layers which were once buried deep within the earth were now exposed. Wind, freezing, thawing, running water and blowing sand continue to shape the landscape even today.
About 100,000 years ago, earth’s climate cooled significantly, and we underwent the ice age that ended about 10,000 years ago. Alpine glaciers began to grow thick in the highest mountain peaks. Under severe weight and with gravity pulling down, glaciers slowly ground their way down mountain valleys scouring away vegetation and soil.
Think about when you’re hiking high in the gore and you see polished pink granite under foot. A glacier once scoured the rock smooth. Or how about when you’re hiking lower in the valley and you come across house-sized rounded boulders. Were these boulders once transported by a glacier?
Glaciers did not carve some mountain valleys, especially if they originate at moderate elevations. These valleys were instead cut by mountain streams. It is easy to tell a stream-cut valley because it is V-shaped. These areas are generally tricky to find a flat spot to camp or picnic because they lack a flat valley floor.
By contrast, a glacial valley is U-shaped and there are plenty of flat spots on the valley floor. The Homestake valley, and the Cross-creek valley are excellent examples of broad glacial valleys. Red Sandstone Creek, Middle Creek or Two Elk Creek are excellent examples of narrow stream cut valleys.
Sometimes there is a combination of features in a high-mountain valley such as in the Gore Range. The highest reaches in the valleys were obviously sculpted by glaciers but in the lower reaches it is not always clear, and some small canyons have been carved into the rock by the streams since the ice age.
It is important to think of landscapes in the context of geologic time. Earth’s rock record suggests that the earth is about 4.5 billion years old. So if you look out at a landscape, ask yourself some questions like, has it been underwater? Has it been a desert? Did tropical plants once grow here? Did giant redwoods grow here? The answer to all these questions is likely yes.
Look out at the landscape again and ask, what evidence has been left behind? By asking ourselves questions about how landscapes evolved, it adds richness to our beautiful mountain views.