Big Thompson Canyon Flood - Climb to Safety! EarthCache
Big Thompson Canyon Flood - Climb to Safety!
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This EarthCache will take you to a location where the effects of the Big Thompson Canyon Flood can be seen. At this site a boardwalk has been built and fish habitat has been reconstructed in a cooperative effort between the U.S. Forest Service, Colorado Division of Wildlife, and several private organizations. This EarthCache is wheelchair accessible through the use of the ramp which is located on the east end of the parking area. GPS reception is poor in the canyon, and can be off by significant fractions of a mile. Therefore, parking is at an asphalt pulloff on the south side of the road at mile marker 72.
Big Thompson Canyon Flood
The Big Thompson Canyon Flood occurred on July 31, 1976. Between approximately 6:30 pm and 10:30 pm, a thunderstorm stalled in the mountains in the upper reaches of the Big Thompson Canyon. Between 10 and 16 inches of rain fell in 4 hours and this caused the river to flow at an estimated 31,000 cubic feet per second (cfs) in the main river below the town of Drake. For comparison, this is over 150 times the normal flow of the river, which is 200 cfs. The resultant flood tore through the canyon destroying homes, businesses, roads, utilities, and the Loveland power plant at Viestenz-Smith Park. The depth of water in some parts of the Narrows was 20 feet; 17 feet deeper than the normal summer depth of 3 feet. The flash flood, which caused damage as far away as the South Platte River near Greeley, took the lives of 144 people. This is considered to be the greatest loss of life due to a natural disaster in Colorado’s history.
New Fish Habitat
Take the steps or ramp down to the boardwalk, then head right for about 50 feet to the west end of the boardwalk. Notice the large granite boulders just upstream and in the center of the river at this point. During the flood, with the river running at over 31,000 cfs, the force of the water was such that boulders this size would have easily been carried down the river. As part of this stream improvement, these rocks now serve to break up the flow of the current and create new habitats in the river. If you look at the boulder in the center of the river, the flow is split and runs on each side. The river then widens out and an eddy in the current is created behind the boulder.
To log this EarthCache, send me an email with the answers to the following questions: 1.) Compare the depth of the river on each side of the boulder versus the depth in the eddy. 2.) Similarly, compare the size of the rock material on each side of the boulder versus the material in the eddy. 3.) What should you do if you are in a canyon during flash flood conditions?
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:
Informational plaques from several memorial sites along the Big Thompson Canyon.
2006. Jarret, R.D., and S.J. Vandas. 1976 Big Thompson Flood, Colorado. USGS Big Thompson Watershed Forum. Big Thompson Canyon Association. USGS General Information Product 35. Online at: (visit link)
1996. Gruntfest, E. What We Have Learned Since The Big Thompson Flood. In: Twenty Years Later: What We have Learned Since the Big Thompson Flood. Proceedings of a Meeting Held in Fort Collins, Colorado, July 13-15, 1996.
Thanks to the Roosevelt National Forest for allowing placement of this EarthCache!
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