Why a Waterfall?
Posted by: 
Volcanoguy
N 44° 11.241 W 111° 19.737
12T E 473709 N 4892734
Sign about the geologic history of the Upper Mesa Falls area.
Waymark Code: WMC89K
Location: Idaho, United States
Date Posted: 08/07/2011
Views: 4
This history sign along walkways leading to Upper Mesa Falls and deals with the geology of the Upper Mesa Falls.
Marker Name: Why a Waterfall?
Marker Type: Roadside
Marker Text:
Two separate volcanic events combined to create Upper Mesa Falls. A volcanic eruption, 1.3 million years ago, covered the area with a thick layer of volcanic ash. Over time the ash compressed into tuff, forming the rock seen across the canyon.
Over hundreds of thousands of years, the river eroded a wide canyon through the tuff. Eventually, basalt lava flows filled the canyon and today provide the resistant rock layer over which the river flows. Aa the falling water erodes the softer tuff below the basalt, large portions of basalt tumble into the river and Upper Mesa Falls slowly recedes upstream.
Did you know?
*Upper Mesa Falls is 114 feet high and approximately 200 feet wide.
*The volume of water flowing over the falls varies seasonally between 387 million to 967 million gallons per day.
*Upper Mesa Falls is the largest undisturbed waterfall in the entire Columbia River system.
County: Fremont
Group Responsible for Placement: U.S. Forest Service
City: Not listed
Date Dedicated: Not listed
Marker Number: Not listed
Web link(s) for additional information: Not listed
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Visit Instructions:
In your log, please say if you learned something new, and if you took any extra time to explore the area once you stopped at the historic marker waymark.
If possible please post a photo of you OR your GPS at the marker location.
Also if you know of any additional links not already mentioned about this bit of Idaho history please include that in your log.