How Old Are the Rocky Mountains?

Mountains of Colorado | Alexey Kamenskiy

If your dad was answering this question, he would probably just say, “old.” And leave it at that. But an answer like this is meaningless to the thoughtful mountaineer, geologist, or outdoor enthusiast with an active mind. The real answer is a bit harder to pin down. The real answer, it turns out, it all about what scale you decide to use.

The Rocky Mountains can be described as true ancients … with a good portion of their crust being made up of rock that is over 1 billion years old. On the other hand, the Rockies can also be thought of as true younglings in the geologic sense, as some of the sub-ranges that make up the Rocky Mountain System are less than 100 million years old. That might sound ancient to us human beings, but in geologic terms, it is a few blinks of the eye.

You can also compare it to the Appalachian Mountains which are about 480 million years old … more than double the age of our young Rockies.

The Rising and Falling of Mountains

First snow Morning at Moraine Lake in Banff National Park Alberta Canada | Michal Balada

The Rocky Mountains are but the newest occupants of their prime real estate down the center of North America. Before the Rockies existed, there was a large sea atop many layers of sediment, and before that, there was a different mountain range altogether. This original mountain range was probably not as big or dramatic as our Rocky Mountains are, but they must have been considerable.

As these “Ancestral Rockies” slowly eroded into sediment and mud, sea waters moved in and covered the entire area with ocean. This was all happening on top of two massive continental plates that had become subducted, that is, one of them started sliding under the other and began to push it up. There was also something of a “crinkling” effect as surface land was also pushed inward by these forces.

The result was a bulge of earth and rock that rose up over the course of several hundred million years. As it rose, rains fell and forms rivers, lakes, and glaciers that carved the Rockies into their current shape.

The Ancestral Rockies Return

Red Sandstone in Roxborough State Park in Colorado | konradrza

While many of the most popular mountain destinations in the Rockies are relatively young, it is still possible to trace the full age of this incredible formation with the very palm of your hand.

In certain segments of the Rocky Mountains, the ground has been pushed  up so far that the ancient sediment has broken through in the form of massive sandstone spikes and ridges. These formations (Colorado’s Red Rocks Park is a prime example) are made of the same material that made up the mountains that existed before the Rocky Mountains were even there.

In some cases, these large visible chunks of the Ancestral Rockies can be as old as 1.7 billion years.

How Old Will the Rockies Get?

Pink Sunset on Snowy Wilson Peak. The San Juan Range, Rocky Mountains, Colorado. | Tobin Akehurst

While there are certainly parts of the Rocky Mountain region that are still swelling upwards (we’re talking centimeters per century) it is difficult to predict how long this trend will last. In addition, the erosion engines of rain, ice, glaciers, and wind tend to act faster than geologic forces.

Considering that the current incarnation of the Rocky Mountains is about 100 million years old, it is probably safe to say that we’ve got at least that much time left to enjoy these beauties before they’re too eroded to be considered mountains.

If it turns out that we’re wrong with that prediction, wait a few hundred million years and let us know in the comments.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.