How the Rockies Rose

The mountains framing the western horizon are far younger than the rock they are made of, which is one of the stranger facts in Colorado geology. The uplift that built the Front Range happened during an event geologists call the Laramide Orogeny, which began in the Late Cretaceous roughly eighty million years ago and wound down around fifty-five million years ago. During that long squeeze, thick slabs of ancient basement rock were thrust upward along deep, steep faults.

The result is what specialists call a basement-cored uplift, and it explains why so much of the exposed stone in the Front Range is granite and metamorphic rock rather than younger sediment. Some of that basement rock is more than a billion years old. The granite at the heart of Pikes Peak, for example, intruded as molten rock about one billion eighty million years ago, then sat buried for ages before being lifted into the sky.

The sheer Diamond face of Longs Peak is made of the same kind of Precambrian granite, raised during that same mountain-building era. The uplift did not act alone. Once the slabs were lifted, water, ice, and time went to work, carving the canyons and exposing the ancient cores we see today.

An even older range, which geologists call the ancestral Rockies, had risen and worn away in this same region hundreds of millions of years before the Laramide event, leaving behind the red sediment that now tilts up against the modern front. So when you look at these peaks, you are seeing very old rock in a relatively new arrangement, the latest chapter in a place that has built mountains more than once.