Pluck and Sculpt: A Few Words On Rocky Mountain Geology

Large rock next to Zig-Zag Trail on Mt. Werner - September 2024

Lichen rock in Fish Creek valley - Sept 2021

​Blue sky, orange and golden aspen shimmering in the breeze, trail underfoot carpeted with fallen leaves. It is easy and a delight to be very caught up in the beauty of our current autumn days. Once in a while, though, whether I’m on the mountain, near Fish Creek, or somewhere else, my eyes are magnetically pulled to the gargantuan boulders along the way. Some charcoal grey, some covered in lime lichen, some with patches of coral pink. They are strewn about randomly - how did they get there? 

About 1.8 million years ago, ice formed and began to sculpt the Rocky Mountain landscape.  Glaciers moved from mountain summits to valley floors. Along the way, these rivers of ice exerted immense pressure on the rock walls of the canyons. As water froze and thawed in cracks in the rock, this effectively allowed pressure from the moving glaciers to pull immense chunks away from the canyon wall in a process called plucking. The massive boulders moved with the flow of the ice and when the glaciers receded, the boulders were left behind, scattered through the landscape like a giant’s marble toss. In another process called abrasion, rocks embedded in the glacier ice scraped against canyon walls, leaving striations as evidence of the direction the glacier moved in.

Hiking alongside Fish Creek is one of my favorite things to do. The pioneers called it Fish Creek back in the day because, as you might guess, there were plenty of fish: whitefish and brook trout. Lower Fish Creek Falls, about 283 feet in height, was the result of two glaciers coming together, creating both a hanging valley and the spectacular falls. 

A few miles further on Fish Creek Trail, well beyond the second falls and getting towards Long Lake, the creek meanders through banks thick with brush. Down lower, close to the Sanctuary Trailhead, the honey-moss colored water gurgles its way over and around rocks, even through the frozen days of winter. The sound of the creek is hopeful: new life in the spring, the continued flow through the hot summer and sometimes dry autumn, and its resilient babble under thick snow even in the frozen days of winter. It seems incredible that almost 2 million years ago the powerful forces of alpine glacier, rock, and erosion forged this valley, now thick in conifer and aspen, a place of peace and flowing water.  

Sources

• Ave, Raymond, Backcountry Adventure Guide to the Mount Zirkel Wilderness, pgs 26-27. Mountain Jay Media LLC, 2003.
• White-Crane, Diane, Hiking the ‘Boat II, pgs 41, 46-47. Aspen Tree Press, 2003.

---