Roaring River Alluvial Fan EarthCache
Roaring River Alluvial Fan
-
Difficulty:
-
-
Terrain:
-
Size: 
(other)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
Rocky Mountain National Park is located west of Estes Park and north and east of Grand Lake. This is a fee area of the National Park Service, and costs $30 per vehicle. This fee is covered in the Rocky Mountain National Park Annual Pass, the Rocky Mountain National Park/Arapaho National Recreation Area Annual Pass, and the America the Beautiful Pass. Please see the following website (visit link) for the entire fee schedule. The park is open 24 hours a day, 365 days a year. Road and Trail Conditions and Closures can be found at: (visit link) Recorded information for the condition of Trail Ridge Road can be found by calling (970) 586-1222. Please remember that all geologic features within the borders of Rocky Mountain National Park are protected by law, as are all natural and historic features. Please do not disturb, damage, or remove any rocks, plants, or animals.
Not all of the geological features you will see in the Park are millions, or even thousands of years old. The alluvial fan at this location was caused by the failure of Lawn Lake Dam less than 30 years ago. This 2-part EarthCache will take you onto the fan where you can see some of the effects of this spectacular debris flow.
Stop 1: N 40 24.670 W 105 38.064 - Mouth of the Roaring River
Lawn Lake Dam was built at approximately 10,900’ in the early 1900s to provide high elevation water storage for cities and irrigation companies along the Big Thompson River drainage. It was a 26’ high earthen dam that had been built near the headwaters of the Roaring River. When it failed in July of 1982, it sent almost 700 acre-feet of water from Lawn Lake down the river at a peak flow which was estimated at about 18,000 cubic feet per second. The river channel was deeply scoured as the force of the water picked up sand, gravel, and boulders (the largest boulder, at 14’ x 17’ x 21’, is estimated to have weighed about 450 tons!) on its way down the mountain. The resulting alluvial fan at this location, covers over 42 acres and is up to 44’ deep.
1.) How many gallons of water were released from the dam’s failure?
2.) Looking up the channel of the Roaring River, estimate the depth of the cut that the river has made which you can see from this point.
Stop 2: N 40 24.643 W 105 38.140 - The Edge of the Fan
An alluvial fan is formed from material which is carried in streams which travel through restricted areas such as canyons or narrow washes. When the water reaches the end of the restriction, the water spreads out and the energy of the water is dissipated. With the reduction of energy in the water, the material which was carried along drops out, with the larger material dropping first.
3.) Compare the sediments (sand, gravels, and boulders) at this location with the sediments from Stop 1. Which area has the larger sediments? Are there other differences that you can see?
To receive credit for this EarthCache, send me an email with the answers to the following question:
1.) How many gallons of water were released from the dam’s failure?
2.) Looking up the channel of the Roaring River, estimate the depth of the cut that the river has made which you can see from this point.
3.) Compare the sediments (sand, gravels, and boulders) at Stop 2 with the sediments from Stop 1.
Please consider posting photos of yourself, or the local geology, when you log this EarthCache. Photos can be an additional rewarding part of your journey, but posting them is not a requirement for logging this EarthCache, and is strictly optional.
The above information was compiled from the following sources:
2004. Rocky Mountain National Park. In Harris, A.G. et al., editors. Geology of National Parks, Sixth Ed. P. 337-356. Dubuque, Iowa: Kendall/Hunt Publishing Company.
Cole, J.C., and Braddock, W.A. 2009. Geologic map of the Estes Park 30’ x 60’ quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3039, 1 sheet, scale 1:100,000, 1 pamphlet, 56 p.
Colorado Geological Survey. 2003. Messages in Stone. Matthews et al., editors. Denver, Colorado.
KellererLynn, K. 2004. Rocky Mountain National Park. Geologic Resource Evaluation Report. NPS D307, September 2004. Online at: (visit link)
Rocky Mountain National Park. Online at: (visit link)
Informational signage at the site.
Rocky Mountain National Park was most helpful in the background discussion, aid in the choosing of sites, and review of this EarthCache. My thanks to the Park for allowing the placement of this EarthCache!
Additional Hints
(No hints available.)