Why the leaves change in Colorado each fall and where to expect peak autumn colors

Morgan Tilton

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The Maroon Bells and Maroon Lake during fall foliage in Colorado.Photo by Scott Mecum.

From September to early October, the flying aspen colors take off at higher elevations and in northern Colorado.

Other deciduous, leaf-changing plants across the Centennial State include Rocky Mountain maple shrubs, cottonwood and willow trees, and alpine tundra.

Though, the shifting aspens draw the most attention statewide.

What causes the fall colors in quaking aspen trees

Groves of quaking aspen generally sit at elevations of 5,000 to 12,000 feet, reports the U.S. Forest Service.

The color change is triggered by the longer nights, Scott Aker, Gardens Unit Leader at the United States National Arboretum, said in a statement.

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Fall foliage near McClure Pass in the Colorado Rocky Mountains.Photo by Andrew Kratz.

The green of aspen leaves reflects the chlorophyll, which is naturally produced by plants and enables photosynthesis.

Photosynthesis is when plants create oxygen and energy (in the form of sugar) through processing sunlight, water, and carbon dioxide, according to the National Geographic Society.

When the exposure to sunlight shortens, the cells of the leaves die then block photosynthesis. The green color fades to reveal underlying hues.

In addition to shorter days, the foliage transformation is influenced by overall tree health, drought, or an uptick in precipitation, reports the Colorado State Forest Service, an agency of the Warner College of Natural Resources at Colorado State University.

As mentioned, the elevation and the latitude also play a role in the evolving tones.

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Fall foliage in the central Rocky Mountains.Photo by Andrew Kratz.

Where to find the best fall colors

The strongest autumn colors follow a wet growing season, and dry and sunny autumn with frost-free but cool nights, according to the United States National Arboretum.

“The ideal conditions are warm, sunny days and cool nights with little wind or drought stress,” added Aker.

Also, the healthier the trees, the more vibrant the pigments will be, and the longer the leaves will hold in the fall season, outlines the Colorado State Forest Service, which also provides an outline of the average peak viewing dates for planning ahead. Dive into the specifics below:

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The fall colors at Shallow Creek west of Creede, Colorado.Photo by the U.S. Department of Agriculture.

The average peak viewing dates

Denver folks, you’ll typically see the peak colors in your backyard first.

From mid to late September, the foliage generally peaks across the northernmost upper-third of the state. We can typically expect the trees to peak at the latitude of central Denver and everywhere north of the Mile High City.

In late September, the peak will usually occur the central third of the state: Glenwood Springs and everywhere southward including Grand Junction, Colorado Springs, and Gunnison.

By late September and early October, we will likely see the colors peak from Pueblo to Alamosa and all the way to the border.

Benefits of fallen foliage each autumn

As the leaves fall, the process is healthy for the ecosystem.

The leaves create a barrier on top of the soil that protects seeds for germination next spring, holds in moisture and helps to prevent erosion, according to the Sustainable Forestry Initiative.

The nutrients from the dead leaves also provide nourishment for the seedlings.

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Adventure journalist Morgan Tilton covers the outdoors with a focus on travel, industry news and human endurance. Featured in more than 70 publications, she’s a recipient of more than a dozen North American Travel Journalists Association awards.

Crested Butte, CO
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