Fall Colors Usher in Autumn in the Rocky Mountains

Posted by Andrew Kratz, US Forest Service Regional Botanist, Rocky Mountain Region

Aspen forest shifts from green to many shades of yellow and orange as fall arrives near McClure Pass
Aspen forest shifts from green to many shades of yellow and orange as fall arrives near McClure Pass. Photo credit: Courtesy of Andrew Kratz.

In Colorado, fall arrives in different ways and at different times around the state.

It generally starts in the high country during August, where green alpine tundra begins to show reds, yellows and browns; colors which persist through the first snow storms of mid-September.  Fall colors move downslope with cold air drainage along streams, where willows turn yellow, followed by the cottonwoods along the rivers which carve their way through the mountains. By September, aspen forests turn to shimmering gold, starting in the upper montane and shifting quickly to lower elevations within the mountains.

By October, trees showing yellow and a few dark reds are sprinkled among the many still green trees in cities like Denver along the western edge of the Great Plains. The grasslands of the eastern plains have generally turned to straw colors in the drought of late summer, but with cold nights the shrubs and trees along creeks and rivers provide yellow, orange and red highlights.

Some wildflowers continue to bloom in fall. They tend to be on warmer, south facing slopes, and tend to be few and scattered. The arctic gentian (Gentiana algida) is one of the late bloomers, starting in very late summer and still blooming well after most plants in the alpine tundra have shut down for the season. The common harebell (Campanula rotundifolia) at low to medium elevations is another wildflower that still has occasional blossoms in the fall.

Fall can be a spectacular time of year here, with gorgeous colors set against a dusting of white snow on the higher peaks and the occasional late blooming wildflower. Fall scenery usually changes quickly, and is subject to high winds or a sudden hard freeze. Fall reminds us that winter is just around the corner.

The arctic gentian (Gentiana algida) flowers from late summer into the fall
The arctic gentian (Gentiana algida) flowers from late summer into the fall. Photo by Andrew Kratz.

Wood’s rose (Rosa woodsii) adds a splash of red leaves under the yellow canopy within an aspen stand.
Wood’s rose (Rosa woodsii) adds a splash of red leaves under the yellow canopy within an aspen stand. Photo by Andrew Kratz.