It seems that no matter what part of the Rocky Mountains you are traveling through, you will be overcome with an incredible and unassailable sense of history. Indeed one feels overwhelmed with ghost-like recollections of the prospectors and trappers that settled this wild country, or the explorers and warriors that came before them to unlock its mysteries, or even the ancient peoples who lived in cities carved into the rocks themselves.
And yet, with all the timelessness of our imagination, the tale of the Rocky Mountains goes much further back than that. Thinking about the Rockies on a geological time-scale is hard to do for a young species such as ours, but is perhaps the only way to truly understand just how old, unique, and enduring these mountains really are.
Paleozoic: The Mountains that came Before the Rockies
It is difficult to imagine that the stretch of earth now decorated with behemoths like Long’s Peak, Mount Elbert, and Mount Robson was once nothing but an endless expanse of flat lad. What is even more difficult to imagine is that before the Rockies, before all that flat land, there existed an entirely different set of mountains altogether.
This was the age of amphibians, where flowering ferns and thick mosses grew up the sides of impossibly massive trees. These trees forms forests that covered the continent, and the only inhabitants around were still undergoing a transition from ocean to land. At this point (mid-Paleozoic, for anyone who is keeping track) the first dinosaurs were still ten million years from making an appearance on planet Earth.
The mountains that existed in this period were likely not as impressive as the Rockies, but they would have been in much of the same location. During the millions of years that followed, these proto-mountains were word down by rain and streams until they were nothing but a flat plain.
Early Cretaceous: Colorado’s Red Rocks are Formed
As the surface of present-day North America has turned to flatlands, swamps, and valleys, sand and mud from decaying mountains spread over the land in thick layers. Slowly, impossibly, these layers turned to hard stone. Soon after, sea water began to pour in over the flat land. Over the course of a few thousand years, the landscape turned into an ocean, erasing the final traces of the ancient mountains.
That is, until millions of years later. As the Rocky Mountains came sprouting out of the Earth, the ancient sandstone layers were disturbed, and large sections of them were thrust up into the daylight. Today, the foothills of Colorado’s Front Range are a great place to see the exposed sections of ancient sandstone. This unique geological and aesthetic wonder is often referred to as the Ancestral Rockies, and the term is wholeheartedly accurate. Even today it is possible to find petrified mollusk shells there, or visit the preserved footprint of the Stegosaurus who roamed the area, way back when it was just a swamp.
Late Cretaceous: Things Get Interesting
Towards the end of the Cretaceous period, but before us mammals had begun to thrive, something very interesting began to happen deep beneath the planet’s surface. The common description of “tectonic plates colliding” is not altogether inaccurate, but it does little to express how much remaining mystery there is around this process.
One way or another, a massive dome-shaped chunk of land arose from the sea. This formation was not as jagged, towering, or epic as today’s Rockies. Rather it was quite the opposite: a rounded bulge with surface breaks here and there, but nothing like the cathedral-shaped mountains that we have today.
When we picture this land-mass pushing its way up from beneath the surface, it is hard not to see it happening as a quick and violent process. The truth is less exciting than that: the fastest these mountains could have possibly emerged from the ground is about one foot per century, with the average rate being much, much slower.
The ‘Great Dome’ becomes The Rocky Mountains
The geological uplift would have created something that might be described as a large dome, with a rolling or uneven surface that roughly matched the current location of the Rockies. This is the mass of rock that would become the Rocky Mountains, though it was not yet formed; something like a block of stone that had yet to been given its shape by the sculptor.
Indeed there were two different processes occurring simultaneously that acted to turn this massive dome into the mountains that we now know. The first of course is the upheaval … the force (or forces) that began driving the Rocky Mountains up into the air. While more and more earth scientists are getting on board with theories about how exactly this happened, there is certainly no consensus and there are still plenty of questions to be answered. This is one of the problems of studying a process that began so many millions of years before there was anybody there to see it.
The second process can be referred to as erosion, if for no other reason than to simplify things a bit. As a catch-all, the term erosion in this case includes everything from rainfall to glacial forces. Here is a look at some of the forces that helped sculpt the Rocky Mountains:
Rainfall & Streams
There is little question that rain was one of the most significant forces that acted upon the growing mountains. Water droplets formed high in the sky would contain not only oxygen and various atmospheric gases, but also minerals from previous precipitation cycles. When the rain hits the surface, it carries these elements downwards and re-distributes them. In many cases, certain acids are formed that make the growing rock even more susceptible to erosion.
Streams and rivers cut shapes into the Rocky Mountains more dramatically than perhaps any other force. Over time these movements of water were able to carve deep fissures within the land mass, leading to the stark canyons and steep valleys that the Rockies are known for.
Frost & Ground Ice
As water fell from the skies in the form of snow or rain, it would slowly make its way into the depths of the mountain. As the seasons shifted, the water would freeze, that, and then freeze again in an ongoing process that changed the fundamental structure of the mountain. This is often times the process by which massive chunks of rock are separated from mountainsides.
Glaciers
The widespread glaciation of the Rocky Mountain region is one of the most recent geological activities to occur, starting with the Great Ice Age that predates human history. However, it is not unreasonable to say that this glacial epoch has not yet seen its end, seeing as how there still remain, high in the Rockies, some small glacial remnants.
Glaciers are snow fields that have been allowed by consistently cold climate to grow so massive and freeze so thoroughly that they can act as a single structure. When one of these snow fields achieves enough mass and hardness, it actually begins to move. The movement of a glacier, although incredibly slow from our perspective, is strong enough to carve wondrous shapes into the Earth, and is responsible for a lot of the shape and character of today’s Rocky Mountain National Park.
What the Rockies are Up To Today
On the geological scale, the Rocky Mountains are still in an active state of change, though it is widely agreed that the large bulk of their formative years is behind them. Still there is some tectonic movement, and every few million years there will be some volcanic activity. And still they rise, as the whole center of the North American continent continues to rise. Or perhaps swell is a better word … one that more accurately describes the gradual and gentle nature of it.
One thing is for sure though: erosion acts a lot faster than anything else, and in time (a lot of time) the Rocky Mountains that we know and love will crumble, dissolve, and slide back into the plains from whence they came, making way perhaps for some future mountains that the Earth has not yet conceived.
