|Longs Peak at Rocky Mountain National Park. Courtesy of Wikipedia.|
The park’s geology began about a billion years ago when molten lava formed large amounts of granite in what is now Colorado. About 500 million years ago, the land begin to sink and fill with sediment, forming several rock strata.
Then, some 300 million years ago, the land rebounded. A range known as the Ancestral Rocky Mountains formed. It eroded over a period of 150 million years, covering its stubs in its own sediment. A series of erosion and sandstone/shale formation occurred over the next 220 million years.
The Front Range of the park formed between 80 million and 40 million years ago during the Laramide Orogeny. At that time, two tectonic plates – the Kula and the Farallon – collided with North America’s western coast. As those plates slid under North America, rock set down over the previous billion years bunched up and wrinkled; those “wrinkles” are the mountains we now see.
Immediately after being thrust upward, the park and the rest of the Rockies looked much different than today, as it was a plateau more than 19,000 feet high. Then about 60 million years ago, this plateau began to erode, forming valleys and summits. The peaks today mostly top out in the 14,000-feet range, about a mile lower than the plateau. Hikers can see one of the Front Range’s most prominent 14ers, Longs Peak, via the Bluebird Lake Trail.
Periods of glaciation that started about 1.8 million years ago deeply shaped the park and Rockies into the landscape we know today. U-shaped valleys as well as cirques (concave-shaped valleys) are signs of past glaciers in the area. The last ice age ended around 11,000 years ago, though remnants of some glaciers still remain. One easy and scenic route to see how glaciers shaped the park is the Alberta Falls Trail, where a waterfalls tumbles over a creek that runs from a gorge created by a glacier. You actually can enter that gorge via the Mills Lake Trail.
Learn more about national park day hiking trails in my Best Sights to See at America’s National Parks guidebook.