June 2024


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Sunday, June 16, 2024

Our Natural World: How Old Are Those Hills?

By Doug Nichols
Berthoud Recorder

“As old as the hills” is what some folks say when they mean that something is very old. But, actually how old are those hills, specifically those lofty peaks of the Colorado Front Range, those mountains just to our west?

That is an interesting question, and the answer is not simple. For one thing, the peaks of the Colorado Front Range, including Longs Peak to our west, Mount Evans to the south, and Pikes Peak near Colorado Springs, is a complex of bodies of rock with somewhat differing histories. Let’s focus on Longs Peak, the loftiest of the nearby mountains.
Longs Peak is located within Rocky Mountain National Park, and is included in the newly designated Wilderness Area that includes the park. It is one of Colorado’s “fourteeners,” mountains exceeding 14,000 feet in elevation (there are 53 in the state, six in the Front Range). Longs Peak rises to 14,259 feet (4,346 meters) above sea level, and ranks 15th in the state. It is fourth among “14ers” in the Front Range (it is higher than Pikes Peak, however). Our view of Longs Peak is partially obscured by 13,911-foot Mt. Meeker, just to the southeast (to our left facing the mountains).
So, how old is Longs Peak? The answer depends on whether we are referring to the rock of which it is composed or the snow-capped shape on the western horizon.
Longs Peak is composed of granite that crystallized from molten rock called magma 1.4 billion years ago. The crystalline mass of granite formed a batholith (literally, a deep rock) formally named the Longs Peak-St Vrain batholith. It was exposed by uplift of the Front Range beginning about 40 million years ago. The uplift of the Rocky Mountains was a complicated process in which mountain ranges rose, only to be reduced by erosion to nearly flat plains, and then rose again; the final uplift began about 18 million years ago. As this final uplift and exposure of the batholith continued, the sculpting of Longs Peak began under the forces of erosion. The most effective agent of erosion was icy glaciers that carved away at the rising mass of rock intermittently during the past two million years (the Ice Ages), up until about 12,000 years ago. Erosion continues today at a reduced pace, due to rain and freeze-and-thaw action on the rock of the mountainsides.
So, how old are those hills, or specifically that mighty hill known as Longs Peak? Well, the granite of which it is composed is 1,400 million (1.4 billion) years old, the Colorado Front Range of which it is a part dates back some 40 million years, the Ice Ages that began to sculpt Longs Peak began about two million years ago and the final shape of the mountain as we see it today dates back 12,000 years. You can take your pick!
Other interesting facts about Longs Peak: it is named after Major Stephen Long, who explored Colorado in the 1820s, and its image graces the Colorado state quarter.

Doug Nichols is a Scientist Emeritus with the U.S. Geological Survey and a Research Associate with the Denver Museum of Nature & Science. He is a resident of Berthoud. Send comments to Recorder.Science.Guy@gmail.com.

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