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Your last weekend to hike to the alluvial fan in Rocky Mountain National Park

The debris field at the alluvial fan in Rocky Mountain National Park
The debris field at the alluvial fan in Rocky Mountain National Park
photos by Mary Glass and Josh Bourassa

In the early morning hours of July 15, 1982 a deafening crash woke Rocky Mountain National Park. It was the horrifying sound of the dam on Lawn Lake failing, and the resulting flood which swept through Horseshoe Park on the eastern side of Rocky Mountain National Park caused a chain reaction of devastation that claimed three lives. The tremendous force of 29 million gallons of water tearing down the mountainside loosened enormous boulders and carried them crashing down the hillside dispersing its earthen load in a fan shape debris field across the valley floor. It created one of the most well known alluvial fans in Colorado, and a popular attraction in Rocky Mountain National Park because of its rather unique rocky terrain.

The view of the largest alluvial fan in Rocky Mountain National Park taken from a lookout on Trail Ridge Road.
photo courtesy of Mary Glass and Josh Bourassa

In fall of 2013 severe flooding in Colorado caused a second alluvial fan in Rocky Mountain National Park; not in a new location but right over the alluvial fan created in 1982. The alluvium (the gravel, sand, sediment and silt) from the more recent flood was smaller in nature than the large boulders from 1982, but the resulting effect on Horseshoe Park was no less staggering though happily it claimed no lives. So much debris was deposited on the valley floor that that it blocked the normal flow of the river causing a course change that washed out bridges, picnic areas and sections of Old Fall River Road. As a result of the floods in 2013 Old Fall River Road is now closed for the season (and probably several seasons according to some employees I spoke with as weather and resource restrictions make clean up and reconstruction a slow process).

I recently took a trip to the site though admittedly I did have to look up what an alluvial fan was before my visit as I guess my inner geologist needs a vocabulary brush up. However, any time something is billed as the biggest or the best or the most unique my inner tourist feels inexplicably drawn to it. So on a drive through Rocky Mountain National Park on July 24, 2014, I walked up to the alluvial fan from the lower parking lot. The area was equally amazing in grandeur and detail. The sheer amount of sand and gravel across the valley floor is impressive; it covers everything. Huge piles of sand, gravel and rocks block the road and new pine trees are growing up through soil which looks more like a beach than a high mountain valley. And while dead tree trunks are all too common in this park because of pine beetle kill the ones by the alluvial fan are unique. They are embedded with rocks and debris which must have shot into them with astonishing speed and force during the 2013 flood.

Until July 28 visitors can walk up Old Fall River Road to the lower parts of the alluvial fan (the road is only closed now to motor vehicles), or they can try and follow the old hiking path which leads to the upper waterfall. I say try because the path, like the road, was ravaged by the floods and only bits and pieces remain. We picked our way along the rocky terrain with no major problems seeing chunks of black asphalt here and there which let us know we were at least still heading in the right direction. The walk was easy and mostly flat (whether on the road or the path) just very, very bumpy. However after July 28 construction begins and so visitors will only be able to see this unique feature from lookout points on Trail Ridge Road (the pull-off at Rainbow Curve having one of the best unobstructed view).

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